Image-forming method and developer

ABSTRACT

An image-forming member excellent in the developing ability and printing durability can be obtained and images can be formed without being accompanied by any accumulation of scum in a developing bath used, by developing an image-forming material, in particular, a negative-working image-forming material which comprises a substrate provided thereon with an image-recording layer comprising an infrared light absorber, a polymerization initiator, an ethylenically unsaturated bond-containing monomer and a binder polymer, using a developer which comprises at least one carbonate and at least one hydrogen carbonate, and at least one surfactant selected from the group consisting of nonionic aromatic ether type surfactants represented by the following general formula (1): X—Y—O-(A) n -(B) m —H (wherein X represents an aromatic group; Y represents a single bond or an alkylene group having 1 to 10 carbon atoms; A and B represent groups different from one another and each represents either —CH 2 CH 2 O— or —CH 2 CH(CH 3 )O—; m and n are 0 or an integer ranging from 1 to 100, respectively, provided that n and m cannot simultaneously represent 0 and that when either n or m is 0, n and m cannot represent 1) and anionic surfactants in an amount ranging from 1.0 to 10% by weight; and which has a pH value ranging from 8.5 to 11.5 and an electrical conductivity x falling within the range: 30&lt;x&lt;100 mS/cm.

BACKGROUND OF THE INVENTION

1. Industrial Field of the Invention

The present invention relates to a developer applied to an image-formingmaterial and a method for forming images and more specifically to adeveloper effective for a negative-working image-forming material whichcan directly be converted into a printing plate by scanning the samewith an infrared laser rays on the basis of digital signals outputtedfrom, for instance, a computer or which can be applied to the so-calleddirect plate-making process as well as an image-forming method whichmakes use of the foregoing developer.

2. Description of the Related Art

Considerable progress has recently been made in the laser technologyand, in particular, a high power, small-sized laser capable of emittinglight rays having a wavelength falling within the range of from nearinfrared to infrared has easily commercially been available. Theselasers are quite useful as light sources for recording used when aprinting plate is directly prepared on the basis of digital signalsoutputted from, for instance, a computer (Computer to Plate: hereundersometimes referred to as “CTP”). For instance, a solid state laser and asemiconductor laser emitting infrared rays whose wavelengths fallswithin the range of from 760 to 1200 nm are quite useful because oftheir high power as compared with other lasers emitting light rayshaving wavelengths beyond the foregoing range. For this reason, therehas recently been an increased demand for an image-forming materialquite sensitive to such a laser or an image-forming material whosesolubility in a developer would greatly be changed through theirradiation thereof with the laser light rays.

There has been proposed, as such an image-forming material, those whichmake the most use of a radical addition-polymerization reaction. Thematerial is in general imagewise exposed to laser light rays and thendeveloped with an alkaline aqueous solution to thus give desired images.In this respect, there have been proposed two kinds of developingmethods or a method comprising the steps of heat-treating the imagewiseexposed material and then developing the same and a method comprisingthe step of developing the imagewise exposed material immediately afterthe imagewise exposure without carrying out any heat-treatment. Theformer suffers from a problem in that it requires the use of alarge-sized installation and that the production cost increases since anautomatic developing machine to be used must be equipped with an ovenfor heating. On the other hand, the latter likewise suffers from aproblem in that the radical polymerization of the material through theexposure is not sufficiently accelerated, the exposed area isinsufficient in the degree of curing and therefore, the printingdurability of the resulting printing plate is low as compared with thatobserved for the printing plate prepared according to the former method.However, there has been desired for the development of an effectiveplate-making or developing method free of any heat-treatment since it isquite advantageous for users to omit the use of any oven for heating inthe plate-making method.

In order to impart satisfactory printing durability to the resultingprinting plate using a non-heating plate-making process, it is desirablethat damages of image areas during the step for developing the sameshould be reduced as low as possible. However, it has been reported thatthe development of, for instance, a negative-working image-formingmaterial comprising a photopolymerizable composition requires the use ofa strongly alkaline aqueous solution containing, for instance, potassiumsilicate and having a pH value of higher than 12.5 (see the patentreference 1 listed below) and the use of a developer having such a highpH value arises a problem such that the image area is greatly damagedand the resulting printing plate has insufficient printing durability.Moreover, if such developing treatment is continued over a long periodof time, problems arise such that the activity of the developer mayundergo a variation in, for instance, the concentration of absorbedcarbon dioxide due to changes of environmental conditions such as thecarbon dioxide concentration in the air and the quality of the resultingprinting plate may variously be changed due to the influence of such anincrease in the carbon dioxide concentration and that the components ofthe plate-making material are accumulated in the developing bath to thuscause, for instance, clogging of pipe or duct.

To solve the foregoing problem or to control any reduction of thedeveloping ability of a developer due to any change with time or agingand/or repeated use of the same, there has been proposed a method fordeveloping a layer comprising a light-sensitive resin composition formedon the surface of a glass substrate with a mixed aqueous solutioncontaining sodium carbonate and sodium hydrogen carbonate having a pHvalue of about 10 (see, for instance, the patent references 2 and 3specified below). However, the inventors of this invention applied thesedevelopers to a lithographic printing plate precursor comprising analuminum substrate provided thereon with a light-sensitive layer whichcomprises a thermally polymerizable light-sensitive resin compositionand as a result, they found that the developers never showed anysatisfactory ability of developing the non-image area thereof.

There has also been reported an alkaline developer to which an alkylphenol type surfactant is added for solving the problem concerning thedeveloping ability of a photoresist comprising a pigment dispersedtherein (see the patent reference 4 listed below), but there have notyet been developed any developer having a sufficient developing abilityand capable of providing a printing plate having sufficient printingdurability.

-   Patent Reference 1: Japanese Un-Examined Patent Publication    (hereunder referred to as “J.P. KOKAI”) Hei 8-108621;-   Patent Reference 2: J.P. KOKAI Hei 5-88377;-   Patent Reference 3: J.P. KOKAI Hei 11-65126-   Patent Reference 4: J.P. KOKAI Hei 10-239858

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image-formingmethod which permits the formation of images excellent in printingdurability, stain resistance and resolution even when a printing plateprecursor is free of any heat-treatment after the imagewise exposure tolight, which is not accompanied by any reduction in the developingability with time due to characteristics of a developer used, whichpermits considerable reduction of the amount of scum generated andaccumulated in a developing bath or tank during the development andwhich can treat imagewise exposed printing plate precursors stably overa long period of time.

It is also an object of the present invention to provide a method forforming images from a negative-working image-forming material on whichimages are recorded using an infrared laser, which can ensuresatisfactory resolution and permits the formation of a printing platehaving sufficient strength of images, without using any heat-treatmentof the precursor after the imagewise exposure.

The inventors of this invention have conducted various studies, whiletaking notice of the developer, have found that when incorporating aspecific nonionic surfactant and/or a specific anionic surfactant into acarbonate-containing developer having a pH value of about 10, thedeveloping ability of non-image area is improved and the sufficientdeveloping ability of a developer, the excellent printing durability andstain resistance of the resulting printing plate can be ensured if theelectrical conductivity of the developer exceeds 30 mS/cm, have achievedthe foregoing object and have thus completed the present invention.

According to a first aspect of the present invention, there is provideda developer comprising at least one carbonate and at least one hydrogencarbonate (bicarbonate), and at least one surfactant selected from thegroup consisting of nonionic aromatic ether type surfactants representedby the following general formula (1) and anionic surfactants in anamount ranging from 1.0 to 10% by weight; and having a pH value rangingfrom 8.5 to 11.5 and an electrical conductivity x falling within therange: 30<x<100 mS/cm:X—Y—O-(A)_(n)-(B)_(m)—H  (1)wherein, X represents a substituted or unsubstituted aromatic group; Yrepresents a single bond or an alkylene group having 1 to 10 carbonatoms; A and B are groups different from one another and each representseither —CH₂CH₂O— or —CH₂CH(CH₃)O—; m and n are 0 or an integer rangingfrom 1 to 100, respectively, provided that n and m cannot simultaneouslyrepresent 0 and that when either n or m is 0, n and m cannot represent1.

According to a second aspect of the present invention, there is providedan image-forming method comprising the steps of imagewise exposing anegative-working image-forming material, which comprises a substrateprovided thereon with an image-recording layer containing aninfrared-absorbing material, a polymerization initiator, anethylenically unsaturated bond-containing monomer and a binder polymer,and then developing the imagewise exposed image-forming material with adeveloper comprising at least one carbonate and at least one hydrogencarbonate; containing at least one surfactant selected from the groupconsisting of nonionic aromatic ether type surfactants represented bythe following general formula (1) and anionic surfactants in an amountranging from 1.0 to 10% by weight; having a pH value ranging from 8.5 to11.5; and an electrical conductivity x falling within the range:30<x<100 mS/cm:X—Y—O-(A)_(n)-(B)_(m)—H  (1)wherein, X represents a substituted or unsubstituted aromatic group; Yrepresents a single bond or an alkylene group having 1 to 10 carbonatoms; A and B are groups different from one another and each representseither —CH₂CH₂O— or —CH₂CH(CH₃)O—; m and n are 0 or an integer rangingfrom 1 to 100, respectively, provided that n and m cannot simultaneouslyrepresent 0 and that when either n or m is 0, n and m cannot represent1.

It has been found that the foregoing developer shows an excellentdeveloping ability even under relatively low pH conditions in which thedeveloper is not susceptible to carbon dioxide, permits the reduction ofany damage on image areas to thus improve the printing durability of theresulting printing plate and has an effect of considerably improving theresolution. In addition, it has also been found that the developerlikewise serves as an agent for improving the dispersing ability ofinsoluble components included in the image-recording layer and that itcan significantly reduce the amount of scum accumulated in thedeveloping tank even in the development over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for illustrating an example of the DRMInterference Spectrophotometer for determining the dissolution behaviorsof an image-recording layer.

FIG. 2 is a schematic block diagram showing an example of the method fordetermining the electrostatic capacity used for the evaluation of thepenetration characteristics of a developer into an image-recordinglayer.

BEST MODE FOR CARRYING OUT THE INVENTION

The developer of the present invention and the image-forming methodusing the developer according to the present invention will hereunder bedescribed in more detail. First of all, the developer of the inventionwill be described below in detail.

[Developer]

Particularly important components of the developer are nonionic aromaticether type surfactants having particular structures and anionicsurfactants incorporated into the same.

(Nonionic Aromatic Ether Type Surfactant)

The nonionic aromatic ether type surfactants represented by thefollowing formula (1) used in the developer of the invention will bedetailed below:X—Y—O-(A)_(n)-(B)_(m)—H  (1)wherein, X represents a substituted or unsubstituted aromatic group; Yrepresents a single bond or an alkylene group having 1 to 10 carbonatoms; A and B represent groups different from one another and eachrepresents either —CH₂CH₂O— or —CH₂CH(CH₃)O—; m and n are 0 or integersranging from 1 to 100, respectively, provided that n and m cannotsimultaneously represent 0 and that when either n or m is 0, n and mcannot represent 1.

In the foregoing general formula, the aromatic group represented by Xmay be, for instance, a phenyl group, a naphthyl group or an anthranylgroup. These aromatic groups may have substituents. Such substituentsmay be, for instance, organic groups having 1 to 100 carbon atoms.Examples of such organic groups are the whole of organic groupsdescribed below in connection with the compounds represented by thefollowing general formulas (1-A) and (1-B). In the formula (1), when Aand B are simultaneously present, they may be in the form of random orblock copolymers.

Specific examples of the compounds represented by the formula (1) arethose represented by the following general formulas (1-A) and (1-B):

wherein, R₁ and R₂ represent a hydrogen atom or an organic group having1 to 100 carbon atoms, respectively; p and q represent 1 or 2,respectively; Y₁ and Y₂ represent a single bond or an alkylene grouphaving 1 to 10 carbon atoms, respectively; r and s are 0 or an integerranging from 1 to 100, respectively, provided that r and s cannotsimultaneously represent 0 and that when either r or s is 0, r and scannot represent 1; and r′ and s′ are 0 or an integer ranging from 1 to100, respectively, provided that r′ and s′ cannot simultaneouslyrepresent 0 and that when either r′ or s′ is 0, r′ and s′ cannotrepresent 1.

When p is 2 and R₁ represents an organic group having 1 to 100 carbonatoms, these groups R₁ may be the same or different or a plurality of R₁groups may form a ring together and when q is 2 and R₂ represents anorganic group having 1 to 100 carbon atoms, these groups R₂ may be thesame or different or a plurality of R₂ groups may form a ring together.

Specific example of the foregoing organic groups having 1 to 100 carbonatoms include saturated or unsaturated, linear or branched aliphatichydrocarbon groups and aromatic hydrocarbon groups such as alkyl groups,alkenyl groups, alkynyl groups, aryl groups and aralkyl groups, as wellas alkoxy groups, aryloxy groups, N-alkylamino groups, N,N-di-alkylaminogroups, N-arylamino groups, N,N-di-arylamino groups, N-alkyl-N-arylaminogroups, acyloxy groups, carbamoyloxy groups, N-alkyl-carbamoyloxygroups, N-aryl-carbamoyloxy groups, N,N-di-alkyl-carbamoyloxy groups,N,N-di-aryl-carbamoyloxy groups, N-alkyl-N-aryl-carbamoyloxy groups,acylamino groups, N-alkyl-acylamino groups, N-aryl-acylamino groups,acyl groups, alkoxy-carbonylamino groups, alkoxy-carbonyl groups,aryloxy-carbonyl groups, carbamoyl groups, N-alkyl-carbamoyl groups,N,N-dialkyl-carbamoyl groups, N-aryl-carbamoyl groups,N,N-diaryl-carbamoyl groups, N-alkyl-N-aryl-carbamoyl groups,polyoxyalkylene chains and these organic groups to which polyoxyalkylenechains are bonded. The foregoing alkyl groups may be linear or branchedones.

Preferred R₁ and R₂ may be, for instance, a hydrogen atom, a linear orbranched alkyl group having 1 to 10 carbon atoms, an alkoxy group having1 to 10 carbon atoms, an alkoxycarbonyl group, an N-alkylamino group, anN,N-di-alkylamino group, an N-alkyl-carbamoyl groups, an acyloxy oracylamino group, a polyoxyalkylene chain having about 5 to 20 repeatingunits, an aryl group having 6 to 20 carbon atoms and an aryl groupcarrying a polyoxyalkylene chain bonded thereto and having about 5 to 20repeating units.

In the compounds represented by the general formulas (1-A) and (1-B),the polyoxyethylene chain preferably has 3 to 50 and more preferably 5to 30 repeating units. The polyoxypropylene chain preferably has 0 to 10and more preferably 0 to 5 repeating units. The polyoxyethylene moietiesand the polyoxypropylene moieties may be in the form of a random orblock copolymer.

Examples of the compounds represented by Formula (1-A) includepolyoxyethylene phenyl ether, polyoxyethylene methyl-phenyl ether,polyoxyethylene octyl-phenyl ether and polyoxyethylene nonyl-phenylether.

Examples of the compounds represented by Formula (1-B) includepolyoxy-ethylene naphthyl ether, polyoxyethylene methyl-naphthyl ether,polyoxyethylene octyl-naphthyl ether and polyoxyethylene nonyl-naphthylether.

In the developer, these nonionic aromatic ether type surfactants may beused alone or in any combination.

The developer has a content of the nonionic aromatic ether typesurfactant suitably ranging from 1 to 10% by weight and more preferably2 to 8% by weight on the basis of the weight of the developer. In thisrespect, if the added amount of the surfactant is too small, theresulting developer has a reduced developing ability and a low abilityof solubilizing the components of the image-recording layer, while if itis too large, the resulting developer would reduce the printingdurability of the printing plate thus obtained.

The following are specific examples of the nonionic aromatic ether typesurfactants represented by Formula (1-A) or (1-B):

A—W Y-1

Y-2

Y-3

Y-4

Y-5

Y-6

Y-7

Y-8

Y-9

Y-10

Y-11

Y-12

Y-13

Y-14

Y-15

Y-16

Y-17

Y-18

Y-19

Y-20

Y-21

Y-22

(Anionic Surfactant)

Next, the anionic surfactants used in the developer of the inventionwill be detailed below. The anionic surfactants used in the presentinvention are compounds each having at least one anionic group in themolecule. Such anionic groups may be, for instance, carbonate anions,sulfonate anions, sulfinate anions, sulfate anions, sulfite anions,phosphate anions, anions derived from phosphorous acids, phosphonateanions and anions derived from phosphinic acids, with sulfonate anionsor sulfate anions being preferably used. More specifically, the anionicsurfactants are compounds each having at least one sulfonate or sulfateanion. Preferably, the anionic surfactants are compounds each having atleast one anionic group of sulfonic acid or anionic group of sulfuricacid monoester. More preferably, the anionic surfactants are compoundseach having at least one anionic group of sulfonic acid or anionic groupof sulfuric acid monoester and at least one substituted or unsubstitutedaromatic group.

As such compounds each having at least one anionic group of sulfonicacid or anionic group of sulfuric acid monoester, preferably used hereinare compounds represented by the following general formula (2) or (3):R₁SO₃ ⁻  (2);R₂—O—SO₃ ⁻  (3)

In these formulas, each of R₁ and R₂ represents a substituted orunsubstituted alkyl, cycloalkyl, alkenyl, aralkyl or aryl group.

The alkyl group may be, for instance, one having 1 to 20 carbon atomsand preferred examples thereof are methyl, ethyl, propyl, n-butyl,sec-butyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, hexadecyl andstearyl group.

The cycloalkyl group may be a monocyclic or polycyclic one. Themonocyclic cycloalkyl group may be, for instance, one having 3 to 8carbon atoms and preferred examples thereof are cyclopropyl,cyclopentyl, cyclohexyl and cyclooctyl groups. Examples of thepolycyclic cycloalkyl groups preferably used herein are adamantyl,norbornyl, isobornyl, camphanyl, di-cyclopentyl, α-pinel andtricyclo-decanyl groups.

The alkenyl group may be, for instance, one having 2 to 20 carbon atomsand specific examples thereof preferably used herein are vinyl, allyl,butenyl and cyclohexenyl groups.

The aralkyl group may be, for instance, one having 7 to 12 carbon atomsand specific examples thereof preferably used herein include benzyl,phenethyl and naphthyl-methyl groups.

The aryl group may be, for instance, one having 6 to 15 carbon atoms andspecific examples thereof preferably used herein include phenyl, tolyl,dimethyl-phenyl, 2,4,6-trimethylphenyl, naphthyl, anthryl and9,10-dimethoxy-anthryl groups.

Moreover, the substituents usable herein are monovalent non-metallicatomic groups other than hydrogen atom and preferred examples thereofare halogen atoms (such as F, Br, Cl, I), a hydroxyl group, alkoxygroups, aryloxy groups, acyl groups, amide groups, ester groups, acyloxygroups, carboxyl groups, carboxylate anions or sulfonate anions.

Specific examples of the alkoxy groups as such substituents are thosehaving 1 to 40, preferably 1 to 20 carbon atoms such as methoxy, ethoxy,propoxy, iso-propoxy, butoxy, pentyloxy, hexyloxy, dodecyloxy,stearyloxy, methoxy-ethoxy, poly(ethyleneoxy). and poly(propyleneoxy)groups. Examples of the aryloxy groups are those having 6 to 18 carbonatoms such as phenoxy, tolyloxy, xylyl-oxy, mesityl-oxy, cumenyl-oxy,methoxy-phenyloxy, ethoxy-phenyloxy, chloro-phenyloxy, bromo-phenyloxyand naphthyl-oxy groups. Examples of the acyl groups are those having 2to 24 carbon atoms such as acetyl, propanoyl, butanoyl, benzoyl andnaphthoyl groups. Examples of the amide groups are those having 2 to 24carbon atoms such as acetamide, propionamide, dodecanoic acid amide,palmitic acid amide, stearic acid amide, benzoic acid amide andnaphthoic acid amide groups. Examples of the acyloxy groups are thosehaving 2 to 20 carbon atoms such as acetoxy, propanoyl-oxy, benzoyl-oxyand naphthoyl-oxy groups. Examples of the ester groups are those having1 to 24 carbon atoms such as methyl ester, ethyl ester, propyl ester,hexyl ester, octyl ester, dodecyl ester and stearyl ester groups. Thesubstituent may be any combination of at least two of the foregoingones.

Among the compounds represented by Formula (2) or (3), preferably usedherein include compounds represented by the following formulas (2-a) and(3-a) while taking into consideration the effects of the presentinvention:

wherein, each of R₃ and R₅ represents a linear or branched alkylenegroup having 1 to 5 carbon atoms; each of R₄ and R₆ represents a linearor branched alkyl group having 1 to 20 carbon atoms; p and q represent0, 1 or 2, respectively; Y₁ and Y₂ represent a single bond or analkylene group having 1 to 10 carbon atoms, respectively; n and m are aninteger ranging from 1 to 100, respectively, provided that if n and mare not less than 2, R₃ or R₅ may be selected from at least two kinds ofgroups.

Examples of the compounds represented by Formulas (2) and (3) will begiven below, but the present invention is not restricted to thesespecific examples at all.

In the foregoing specific examples, x and y represent the numbers ofrepeating units or ethyleneoxy chains and propyleneoxy chains,respectively and they are integers each ranging from 1 to 20 (averagevalues).

It is effective to add the compound represented by Formula (2) or (3) tothe developer in an amount suitably ranging from 1 to 10% by weight andpreferably 2 to 10% by weight on the basis of the total weight of thedeveloper.

In this respect, if the added amount of the compound is too small, theresulting developer has a reduced developing ability and a low abilityof solubilizing the components of the light-sensitive layer, while if itis too large, the resulting developer would reduce the printingdurability of the printing plate ultimately prepared.

The compound represented by the general formula (2) or (3) may ingeneral be commercially available. Examples of such compoundscommercially available include those prepared and sold by a variety ofmanufacturers such as Asahi Denka Kogyo K.K.; Kao Corporation; SanyoChemical Industries, Ltd.; New Japan Chemical Co., Ltd.; Dai-Ichi KogyoSeiyaku Co., Ltd.; Takemoto Oil and Fats Co., Ltd.; Toho ChemicalIndustry Co., Ltd.; and NOF corporation.

In addition, the developer used in the plate-making method of theinvention may further comprise other surfactants such as those specifiedbelow in addition to at least one surfactant selected from the groupconsisting of the foregoing nonionic aromatic ether type surfactants andanionic surfactants.

Examples of other surfactants are nonionic surfactants, for instance,polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether,polyoxyethylene cetyl ether and polyoxyethylene stearyl ether,polyoxyethylene alkyl esters such as polyoxyethylene stearate, sorbitanalkyl esters such as sorbitan mono-laurate, sorbitan mono-stearate,sorbitan di-stearate, sorbitan mono-oleate, sorbitan sesqui-oleate andsorbitan tri-oleate, and mono-glyceride alkyl esters such as glycerolmono-stearate and glycerol mono-oleate; anionic surfactants, forinstance, alkyl benzene-sulfonic acid salts such as sodium dodecylbenzene sulfonate, alkyl naphthalene-sulfonic acid salts such as sodiumbutyl naphthalene sulfonate, sodium pentyl naphthalene sulfonate, sodiumhexyl naphthalene sulfonate and octyl naphthalene sulfonate, alkylsulfuric acid salts such as sodium lauryl sulfate, alkyl sulfonic acidsalts such as sodium dodecyl sulfonate, and sulfo-succinic acid estersalts such as sodium di-lauryl sulfosuccinate; and amphotericsurfactants, for instance, alkyl betaines such as lauryl betaine andstearyl betaine, and amino acids. Preferably used herein are anionicsurfactants such as alkyl naphthalene-sulfonic acid salts among others.

These surfactants may be used alone or in any combination. Moreover, thecontent of these surfactants in the developer preferably ranges from 0.1to 20% by weight as expressed in terms of the reduced amount of theeffective component thereof.

The developer used in the image-forming method of the inventioncomprises at least one surfactant selected from the group consisting ofthe nonionic aromatic ether type surfactants and anionic surfactantsdiscussed above in detail in an amount ranging from 1.0 to 10% byweight; further comprises at least one carbonate and at least onehydrogen carbonate; has a pH value ranging from 8.5 to 11.5; and has anelectrical conductivity x falling within the range: 30<x<100 mS/cm. Inthis connection, the pH value and the electrical conductivity aredetermined at ordinary temperature (about 25° C.).

The foregoing at least one carbonate and at least one hydrogen carbonateserve as alkaline agents in the developer. The carbonate may be at leastone compound selected from carbonates of inorganic alkalis. Specificexamples thereof are sodium carbonate, potassium carbonate and ammoniumcarbonate. The hydrogen carbonate may be, for instance, at least onecompound selected from hydrogen carbonates of inorganic alkalis.Specific examples thereof are sodium hydrogen carbonate, potassiumhydrogen carbonate and ammonium hydrogen carbonate. It is preferred thatthe amounts of the carbonate and the hydrogen carbonate in the developerbe adjusted to the range of from 0.005 to 1 mole/L and 0.001 to 1 mole/Lrespectively, since the desired pH buffering effect can be obtainedwithin the pH range of from 8.5 to 11.0 and the amount of carbon dioxideabsorbed by the developer can be reduced.

Moreover, it is essential for the developer that the pH thereof rangesfrom 8.5 to 11.5 and preferably 9.0 to 11.0. In addition, it is alsoessential for the developer to control the electrical conductivity xthereof such that it falls within the range: 30<x<100 mS/cm, preferably31 to 80 mS/cm and more preferably 35 to 60 mS/cm.

Moreover, an alkali metal salt of an organic acid or an alkali metalsalt of an inorganic acid may be added to the developer as aconductivity-adjusting agent to thus control the electrical conductivitythereof.

When the developer comprises alkali metal salts other than a mixture ofa carbonate and a hydrogen carbonate, the developing ability of theresulting developer is reduced due to the elapse of time and/or repeateduse even if the pH and the electrical conductivity thereof are fallwithin the ranges specified above. Further, if the pH value of thedeveloper is lower than the lower limit, the developer never permits theformation of any image, while if it exceeds the upper limit, thedeveloping ability thereof is reduced due to, for instance, thedeterioration through the absorption of carbon dioxide in the air, evenif the developer comprises a mixture of a carbonate and a hydrogencarbonate. On the other hand, if the electrical conductivity of thedeveloper is lower than the lower limit, the resulting developer hardlysolubilizes a layer of an image-forming composition on an aluminumsubstrate and accordingly, any image cannot be formed thereon, while ifit exceeds the upper limit, residual films remain on the non-image areaand the developing ability of the resulting developer is reduced ineither of these cases.

The foregoing developer may be prepared by adding both of alkali metalcarbonate and hydrogen carbonate to water to thus simultaneouslydissolve them or by separately preparing aqueous solutions containingthese components and then admixing these solutions.

The developer may further comprise, as an alkaline agent, an inorganicalkaline agent such as sodium tertiary phosphate, potassium tertiaryphosphate, ammonium tertiary phosphate, sodium borate, potassium borate,ammonium borate, sodium hydroxide, potassium hydroxide, ammoniumhydroxide or lithium hydroxide; and an organic alkaline agent such asmono-methylamine, di-methylamine, tri-methylamine, mono-ethylamine,di-ethylamine, trn-ethylamine, mono-isopropylamine, di-isopropyl-amine,tri-isopropylamine, n-butylamine, mono-ethanolamine, di-ethanolamine,tri-ethanolamine, mono-isopropanolamine, di-isopropanolamine,ethyleneimine, ethylenediamine, pyridine or tetramethyl ammoniumhydroxide. These alkaline agents may be used alone or in any combinationof at least two of them.

The developer may likewise comprise a chelating agent. Examples of suchchelating agents are polyphosphoric acid salts such as Na₂P₂O₇, Na₅P₃O₃,Na₃P₃O₉, Na₂O₄P(NaO₃P)PO₃Na₂ and Calgon (sodium polymetaphosphate);amino-polycarboxylic acids such as ethylenediamine-tetraacetic acid andsodium and potassium salts thereof, diethylenetriamine-pentaacetic acidand sodium and potassium salts thereof, triethylenetetramine-hexaaceticacid and sodium and potassium salts thereof,hydroxyethyl-ethylenediamine-triacetic acid and sodium and potassiumsalts thereof, nitrilo-triacetic acid and sodium and potassium saltsthereof, 1,2-diamino-cyclohexane-tetraacetic acid and sodium andpotassium salts thereof, and 1,3-diamino-2-propanol-tetraacetic acid andsodium and potassium salts thereof; and organic phosphonic acids such as2-phosphonobutane-tricarboxylic acid-1,2,4 and sodium and potassiumsalts thereof, 2-phosphonobutane-tricarboxylic acid-2,3,4 and sodium andpotassium salts thereof, 1-phosphonoethane-tricarboxylic acid-1,2,2 andsodium and potassium salts thereof, 1-hydroxyethane-1,1-diphosphonicacid and sodium and potassium salts thereof, and amino-tri-(methylenephosphonic acid) and sodium and potassium salts thereof. The optimumamount of such a chelating agent to be incorporated into the developermay vary depending on the hardness and amount of water used, but it ingeneral ranges from 0.01 to 5% by weight and more preferably 0.01 to0.5% by weight on the basis of the weight of the developer practicallyused.

The developer of the present invention may if necessary comprise thefollowing components in combination with the foregoing components. Suchoptional components include, for instance, organic carboxylic acids suchas benzoic acid, phthalic acid, p-ethyl-benzoic acid, p-n-propyl-benzoicacid, p-isopropyl-benzoic acid, p-n-butyl-benzoic acid,p-t-butyl-benzoic acid, p-2-hydroxyethyl-benzoic acid, decanoic acid,salicylic acid and 3-hydroxy-2-naphthoic acid; organic solvents such asisopropyl alcohol, benzyl alcohol, ethyl, cellosolve, butyl cellosolve,phenyl cellosolve, propylene glycol and diacetone alcohol; as well aschelating agents; reducing agents; dyes; pigments; water softener; andpreservatives.

The foregoing developer can be used as a developer and a replenisherused for the development of an imagewise exposed negative-workingimage-forming material and it is preferably applied to an automaticdeveloping machine. When developing such materials using an automaticdeveloping machine, the developer is fatigued in proportion to thethroughput and therefore, the processing capacity of the machine may berecovered by the use of a replenisher or a fresh developer. This systemof replenishment is likewise preferably used in the image-making methodof the present invention. The use of the foregoing developer in thedevelopment of the image-forming material as will be detailed below isquite preferred since the effects of the invention become conspicuous.More specifically, the preferred developer of the invention is one forthe development of a negative-working image-forming material whichcomprises a substrate provided thereon with an image-recording layercontaining an infrared absorber, a polymerization initiator, anethylenically unsaturated bond-containing monomer and a binder polymer.

The image-forming material used in the present invention is onecomprising a substrate provided thereon with an optional undercoatinglayer, an image-recording layer and an optional protective layerlaminated in order, wherein the foregoing image-recording layercomprises an infrared absorber, a polymerization initiator, anethylenically unsaturated bond-containing monomer and a binder polymer.

In this respect, the term “laminated in order” means that theundercoating layer, the image-recording layer and the protective layerare formed in this order, the undercoating layer and the protectivelayer may be optional ones and the image-forming material may likewisecomprise other layers (such as intermediate layers, back coating layers)depending on various purposes.

(Infrared Absorber)

The image-recording layer of the image-forming material used in theinvention should comprise an infrared absorber. The infrared absorberserves to convert the absorbed infrared light rays into heat. The heatthus generated thermally decomposes the polymerization initiator(radical-generating agent) as will be detailed later to thus generateradicals. The infrared absorbers used in the invention are preferablydyes or pigments whose wavelengths of absorption maxima fall within therange of from 760 to 1200 nm.

Such dyes may be those commercially available and known ones such asthose disclosed in, for instance, “A Handbook of Dyes” (edited by TheSociety of Organic Synthesis Chemistry in Japan, published in 1960(Showa 45)). Specific examples thereof are azo dyes, metal complex azodyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes,phthalocyanine dyes, carbonium dyes, quinone-imine dyes, methine dyes,cyanine dyes, squarylium dyes, pyrylium dyes and metal thiolatecomplexes.

Examples of preferred dyes are cyanine dyes such as those disclosed in,for instance, J.P. KOKAI Nos. Sho 58-125246, Sho 59-84356, Sho 59-202829and Sho 60-78787; methine dyes such as those disclosed in, for instance,J.P. KOKAI Nos. Sho 58-173696, Sho 58-181690 and Sho 58-194595;naphthoquinone dyes such as those disclosed in, for instance, J.P. KOKAINos. Sho 58-112793, Sho 58-224793, Sho 59-48187, Sho 59-73996, Sho60-52940 and Sho 60-63744; squarylium dyes such as those disclosed in,for instance, J.P. KOKAI Sho 58-112792; and cyanine dyes such as thosedisclosed in, for instance, U.K. Patent No. 434,875.

The near infrared-absorbing sensitizers disclosed in U.S. Pat. No.5,156,938 are also suitably used in the invention and preferably usedherein also include, for instance, substituted arylbenzo(thio) pyryliumsalts disclosed in U.S. Pat. No. 3,881,924; trimethine thia-pyryliumsalts disclosed in J.P. KOKAI Sho 57-142645 (U.S. Pat. No. 4,327,169);pyrylium type compounds disclosed in J.P. KOKAI Nos. Sho 58-181051, Sho58-220143, Sho 59-41363, Sho 59-84248, Sho 59-84249, Sho 59-146063 andSho 59-146061; cyanine dyes disclosed in J.P. KOKAI Sho 59-216146; andpenta-methine thio-pyrylium salts disclosed in U.S. Pat. No. 4,283,475;as well as pyrylium compounds disclosed in J.P. KOKOKU Nos. Hei 5-13514and Hei 5-19702. Examples of other dyes preferably used herein are nearinfrared-absorbing dyes represented by Formulas (I) and (II) in thespecification of U.S. Pat. No. 4,756,993.

Moreover, examples of other dyestuffs preferably used in the inventionare specific indolenine-cyanine dyestuffs disclosed in J.P. KOKAI2002-278057 such as those listed below:

Among these dyes, particularly preferred are cyanine dyestuffs,squarylium dyestuffs, pyrylium salts, nickel-thiolate complexes,indolenine-cyanine dyestuffs. Further, cyanine dyestuffs andindolenine-cyanine dyestuffs are more preferred and particularlypreferred are cyanine dyestuffs represented by the following generalformula (a):

In Formula (a), X¹ represents a hydrogen atom, a halogen atom, —NPh₂,X²-L¹ or a group listed below. In this respect, X² represents an oxygen,nitrogen or sulfur atom and L¹ represents a hydrocarbon group having 1to 12 carbon atoms, a hetero atom-containing aromatic ring or a heteroatom-containing hydrocarbon group having 1 to 12 carbon atoms. In thisregard, the term “hetero atom” means N, S, O, a halogen atom or Se.

X_(a) ⁻ is defined like the substituent Z¹⁻ as will be described later,R^(a) represents a substituent selected from the group consisting of ahydrogen atom, alkyl groups, aryl groups, substituted or unsubstitutedamino groups and halogen atoms.

Each of R¹ and R² independently represents a hydrocarbon group having 1to 12 carbon atoms. R¹ and R² preferably represent hydrocarbon groupseach having at least two carbon atoms because of the storage stabilityof the coating solution for preparing a recording layer and they areparticularly preferably bonded together to form a 5- or 6-membered ring.

Ar¹ and Ar² may be the same or different and each of them represents asubstituted or unsubstituted aromatic hydrocarbon group. Preferredaromatic hydrocarbon groups are, for instance, benzene rings andnaphthalene rings. In addition, examples of preferred substituentsthereof are hydrocarbon groups having not more than 12 carbon atoms,halogen atoms and alkoxy groups having not more than 12 carbon atoms. Y¹and Y² may be the same or different and each represents a sulfur atom ora dialkyl-methylene group having not more than 12 carbon atoms. R³ andR⁴ may be the same of different and each represents a substituted orunsubstituted hydrocarbon group having not more then 20 carbon atoms.Examples of preferred substituents thereof are alkoxy groups having notmore than 12 carbon atoms, carboxyl group and sulfo group. R⁵, R⁶, R⁷and R⁸ may be the same of different and each represents a hydrogen atomor a hydrocarbon group having not more then 12 carbon atoms andpreferably a hydrogen atom because of the easy availability of thestarting material. Z¹⁻ represents a counter anion. In this respect,however, Z¹⁻ is not needed when the cyanine dyestuff of Formula (a)includes an anionic substituent within the structure thereof and it isnot necessary to neutralize the charges. Examples of Z¹⁻ preferably usedherein are a halogen ion, a perchlorate ion, a tetrafluoro-borate ion, ahexafluoro-phosphate ion and a sulfonate ion because of the storagestability of the coating solution for preparing a recording layer andparticularly preferably a perchlorate ion, a hexafluoro-phosphate ionand an aryl-sulfonate ion.

Specific examples of the cyanine dyestuffs represented by Formula (a)preferably used in the invention are those disclosed in Sections 17 to19 of J.P. KOKAI 2001-133969.

Moreover, particularly preferred other examples thereof are specificindolenine-cyanine dyestuffs disclosed in J.P. KOKAI 2002-278057described above.

The pigments usable in the present invention are commercially availableones and those disclosed in A Handbook of Color Index (C.I.), “AHandbook of Up-To-Date Pigments” (edited by Society of PigmentTechnology Japan, published in 1977), “Up-To-Date Pigments ApplicationTechnology” (CMC Publishing Co., Ltd., published in 1986) and “PrintingInk Technology” (CMC Publishing Co., Ltd., published in 1984).

Examples of pigments include black pigments, yellow pigments, orangepigments, brawn pigments, red pigments, purple pigments, blue pigments,green pigments, fluorescent pigments and metal powder pigments, as wellas polymer-bonded dyestuffs. Specific examples thereof are insoluble azopigments, azo lake pigments, condensed azo pigments, chelate azopigments, phthalocyanine type pigments, anthraquinone type pigments,perylene and perinone type pigments, thioindigo type pigments,quinacridone type pigments, dioxazine type pigments, iso-indolinone typepigments, quinophthalone type pigments, printing lake pigments, azinepigments, nitroso pigments, nitro pigments, natural pigments,fluorescent pigments, inorganic pigments and carbon black. Among thesepigments, preferably used herein is carbon black.

These pigments may be used without any surface treatment or may besubjected to such a treatment. Examples of methods for such surfacetreatment are one in which the surface of the pigment is coated with aresin or wax; a method comprising adhering a surfactant to the pigment;and a method in which a reactive substance (such as a silane couplingagent, an epoxy compound, a poly(isocyanate)) is linked to the surfaceof the pigment. The foregoing surface-treating methods are disclosed in“Properties and Applications of Metal Soap” (Saiwai Shobo), “PrintingInk Technology” (CMC Publishing Co., Ltd., published in 1984) and“Up-To-Date Pigments Application Technology” (CMC Publishing Co., Ltd.,published in 1986).

The particle size of the pigment preferably ranges from 0.01 to 10 μm,more preferably 0.05 to 1 μm and particularly preferably 0.1 to 1 μm. Ifthe particle size of the pigment is less than 0.01 μm, the dispersedsubstances have insufficient stability in the coating solution forforming the image-recording layer, while if it exceeds 10 μm, theresulting image-recording layer would show insufficient uniformity.

The method for dispersing the pigment in the coating solution may be anyknown one used in the preparation of ink or toners. Examples ofdispersing machines are an ultrasonic dispersing machine, a sand mill,an attritor, a pearl mill, a super mill, a ball mill, an impeller, adisperser, a KD mill, a colloid mill, a dynatron, a three-roll mill, anda press kneader. The details thereof are disclosed in “Up-To-DatePigments Application Technology” (CMC Publishing Co., Ltd., published in1986).

When these infrared absorbers are added to the image-recording layer,they may be added to a layer simultaneous with other components or theymay be added to a separate layer, but when preparing a negative-workinglithographic printing plate precursor as a negative-workingimage-recording material, they are added to the layer in such a mannerthat the absorbance of the image-recording layer (light-sensitive layer)observed at the maximum absorption wavelength ranging from 760 to 1200nm falls within the range of from 0.5 to 1.2 as determined by thereflection-determination method. The absorbance thereof preferablyranges from 0.6 to 1.15. If the absorbance is beyond the range specifiedabove, the strength of the image area is reduced and the number ofprinted matters upon printing operation is accordingly reduced. Thereason therefor is not clearly elucidated, but it would be assumed thatif the absorbance is less than 0.5, the image-recording layer cannotsufficiently absorb infrared light rays applied and as a result, theradical polymerization reaction insufficiently proceeds in the overallimage-recording layer. On the other hand, it would likewise be assumedthat if the absorbance is higher than 1.2, only the outermost layer ofthe image-recording layer absorbs infrared light rays and the infraredlight rays applied do not reach the area in the proximity to thesubstrate. As a result, any radical polymerization does not take placein the vicinity to the substrate and the adhesion between the substrateand the image-recording layer becomes correspondingly insufficient.

The absorbance of the image-recording layer can be controlled byappropriately adjusting the amount of the infrared absorber to be addedto the image-recording layer and the thickness of the layer. Theabsorbance can be determined according to the usual method. Examples ofsuch determination methods are a method comprising the steps of forming,on a reflective substrate such as an aluminum substrate, animage-recording layer having a thickness properly determined in such amanner that the coated amount as determined after drying would fallwithin the range required for forming a lithographic printing plate anddetermining the reflected light density using an optical densitometerand a method comprising determining the absorbance using aspectrophotometer according to the reflection method which makes use ofan integrating sphere.

(Polymerization Initiators)

The image-recording layer used in the invention comprises apolymerization initiator for initiating and promoting the curingreaction of a polymerizable compound as will be described below. Suchpolymerization initiators may be, for instance, sulfonium saltpolymerization initiators serving as thermal decomposition type radicalgenerators which are thermally decomposed to thus generate radicals.

In the present invention, when such a sulfonium salt polymerizationinitiator is used simultaneously with the foregoing infrared absorberand the image-recording layer is irradiated with an infrared laser, theinfrared absorber generates heat and the heat in turn permits thegeneration of radicals. In the present invention, such a combinationwould permit the heat-mode recording in high sensitivity.

Examples of such sulfonium salt polymerization initiators suitably usedin the invention include onium salts represented by the followinggeneral formula (I):

In the general formula (I), R¹¹, R¹² and R¹³ may be the same ordifferent and each represents a substituted or unsubstituted hydrocarbongroup having not more than 20 carbon atoms. Examples of preferredsubstituents are halogen atoms, nitro groups, alkyl groups having notmore than 12 carbon atoms, alkoxy groups having not more than 12 carbonatoms or aryloxy groups having not more than 12 carbon atoms. Z¹¹⁻represents a counter ion selected from the group consisting of halogenions, perchlorate ions, tetrafluoro-borate ions, hexafluoro-phosphateions, carboxylate ions and sulfonate ions, with perchlorate ions,hexafluoro-phosphate ions, carboxylate ions and aryl-sulfonate ionsbeing preferably used herein.

The following are specific examples of such onium salts ([OS-1] to[OS-10]), but the present invention is not restricted to these specificexamples at all:

In addition to the onium salts listed above, preferably used herein alsoinclude, for instance, specific aromatic sulfonium salts such as thosedisclosed in J.P. KOKAI Nos. 2002-148790, 2002-350207 and 2002-6482.

The image-recording layer used in the invention may further compriseother polymerization initiator (other radical generators) simultaneouswith the foregoing sulfonium salt polymerization initiator as anessential component.

Examples of such other radical generators are onium salts other thansulfonium salts, triazine compounds having a trihalomethyl group,peroxides, azo polymerization initiators, azide compounds,quinone-diazide, oxime ester compounds and triaryl monoalkyl-boratecompounds. Among these, onium salts are preferred because of their highsensitivity.

Examples of other onium salts suitably used in the invention areiodonium salts and diazonium salts. In the present invention, theseonium salts do not serve as acid-generators, but serve as radicalpolymerization initiators.

Examples of other onium salts usable in the invention include thoserepresented by the following general formulas (II) and (III):Ar²¹—I⁺—Ar²²Z²¹⁻  General Formula (II):Ar³¹—N⁺≡NZ³¹⁻  General Formula (III):

In Formula (II), each of Ar²¹ and Ar²² independently represents asubstituted or unsubstituted aryl group having not more than 20 carbonatoms. When the aryl group is a substituted one, examples of preferredsubstituents include halogen atoms, nitro groups, alkyl groups havingnot more than 12 carbon atoms, alkoxy groups having not more than 12carbon atoms, or aryloxy groups having not more than 12 carbon atoms.Z²¹⁻ is a counter ion identical to that listed above in connection withZ¹¹⁻.

In Formula (III), Ar³¹ represents a substituted or unsubstituted arylgroup having not more than 20 carbon atoms. Examples of preferredsubstituents thereof are halogen atoms, nitro groups, alkyl groupshaving not more than 12 carbon atoms, alkoxy groups having not more than12 carbon atoms, aryloxy groups having not more than 12 carbon atoms,alkylamino groups having not more than 12 carbon atoms, di-alkylaminogroups having not more than 12 carbon atoms, arylamino groups having notmore than 12 carbon atoms, or di-arylamino groups having not more than12 carbon atoms. Z³¹⁻ is a counter ion identical to that listed above inconnection with Z¹¹⁻.

The following are specific examples of onium salts ([OI-1] to [OI-10])represented by Formula (II) and onium salts ([ON-1] to [ON-5])represented by Formula (III), preferably used in the present invention,but the present invention is not restricted to these specific examplesat all:

Specific examples of onium salts suitably used as polymerizationinitiators (radical generators) in the invention are those listed inJ.P. KOKAI 2001-133696.

In this respect, the polymerization initiator (radical generators) usedin the invention preferably has a maximum absorption wavelength of notmore than 400 nm and more preferably not more than 360 nm. The use ofsuch an absorption wavelength thus shifted toward the ultraviolet regionwould permit the handling of the image-forming material under theirradiation with white light rays.

The total content of the polymerization initiator in the image-recordinglayer used in the invention ranges from 0.1 to 50% by weight, preferably0.5 to 30% by weight and particularly preferably 1 to 20% by weight onthe basis of the total weight of the solid contents. If the contentthereof is less than 0.1% by weight, the resulting layer has a reducedsensitivity, while if it exceeds 50% by weight, there is observed such atendency that when the recording layer is applied to a lithographicprinting plate precursor, the non-image area of the resulting printingplate easily causes staining during printing operations.

A single polymerization initiator or any combination of at least twosuch initiators may be used in the invention insofar as it comprises asulfonium salt polymerization initiator as an essential component. Incase where at least two polymerization initiators are used incombination, they may simply comprise a plurality of sulfonium saltpolymerization initiators or they may be mixtures of sulfonium saltpolymerization initiators and other polymerization initiators.

When using a combination of a sulfonium salt polymerization initiatorand another polymerization initiator, the mixing ratio (by weight) ofthe former to the latter preferably ranges from 100/1 to 100/50 and morepreferably 100/5 to 100/25.

Moreover, the polymerization initiator is incorporated into theimage-recording layer and the initiator may be added to a layersimultaneous with the other components or to a separate layer.

(Ethylenically Unsaturated Bond-Containing Monomers)

The image-recording layer usable in the present invention comprises anethylenically unsaturated bond-containing monomer. The monomer is anaddition-polymerizable compound having at least one ethylenicallyunsaturated bond in the molecule and it may be selected from the groupconsisting of such compounds having at least one, preferably at leasttwo ethylenically unsaturated bonds in the molecule. Various groups ofsuch compounds have widely been known in this art and they may be usedin the invention without any particular restriction. They may be in avariety of chemical forms such as monomers; prepolymers or dimmers,trimers and higher oligomers; or mixture thereof; and copolymersthereof. Examples of such monomers and copolymers thereof areunsaturated carboxylic acids (such as acrylic acid, methacrylic acid,itaconic acid, crotonic acid, isocrotonic acid and maleic acid) andesters and amides thereof and preferably used herein are, for instance,esters of unsaturated carboxylic acids with aliphatic polyhydricalcohols and amides of unsaturated carboxylic acids with aliphaticpolyvalent amine compounds. Suitably used herein also include, forinstance, addition reaction products of unsaturated carboxylic acidesters or amides carrying a nucleophilic substituent such as hydroxyl,amino and/or mercapto groups with mono-functional or multi-functionalisocyanates or epoxides; and dehydration-condensation reaction productsof the foregoing esters or amides with mono-functional ormulti-functional carboxylic acids. Suitably used herein likewiseinclude, for instance, addition reaction products of unsaturatedcarboxylic acid esters or amides carrying an electrophilic substituentsuch as isocyanate and/or epoxy groups with mono-functional ormulti-functional alcohols, amines and/or thiols; and substitutionreaction products of unsaturated carboxylic acid esters or amidescarrying a releasable substituent such as halogen atoms and/or tosyl-oxygroup with mono-functional or multi-functional alcohols, amines and/orthiols. Examples of such monomers usable herein further include theforegoing compounds in which the foregoing unsaturated carboxylic acidsare replaced with unsaturated sulfonic acids, styrene and/or vinylethers.

Specific examples of ester monomers of aliphatic polyhydric alcoholswith unsaturated carboxylic acids are acrylic acid esters such asethylene glycol diacrylate, triethylene glycol diacrylate,1,3-butanediol diacrylate, tetramethylene glycol diacrylate, propyleneglycol diacrylate, neopentyl glycol diacrylate, trimethylolpropanetriacrylate, trimethylolpropane tri(acryloyl-oxy-propyl) ether,trimethylol-ethane triacrylate, hexane-diol diacrylate,1,4-cyclohexane-diol diacrylate, tetraethylene glycol diacrylate,pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritoltetra-acrylate, di-pentaerythritol diacrylate, di-pentaerythritolhexa-acrylate, sorbitol triacrylate, sorbitol tetra-acrylate, sorbitolpenta-acrylate, sorbitol hexa-acrylate, tri(acryloyl-oxy-ethyl)isocyanurate, and polyester acrylate oligomers.

Specific examples of ester monomers include methacrylates such astetramethylene glycol di-methacrylate, triethylene glycoldi-methacrylate, neopentyl glycol di-methacrylate, trimethylolpropanetri-methacrylate, trimethylol-ethane tri-methacrylate, ethylene glycoldi-methacrylate, 1,3-butanediol di-methacrylate, hexane-dioldi-methacrylate, pentaerythritol di-methacrylate, pentaerythritoltri-methacrylate, pentaerythritol tetra-methacrylate, di-pentaerythritoldi-methacrylate, di-penta-erythritol hexa-acrylate, sorbitoltri-methacrylate, sorbitol tetra-methacrylate,bis[p-(3-methacryloxy-2-hydroxy-propoxy) phenyl]dimethyl methane andbis[p-(methacryloxy-ethoxy)phenyl]dimethyl-methane.

Specific examples of ester monomers include itaconates such as ethyleneglycol di-itaconate, propylene glycol di-itaconate, 1,3-butanedioldi-itaconate, 1,4-butanediol di-itaconate, tetramethylene glycoldi-itaconate, pentaerythritol di-itaconate, and sorbitoltetra-itaconate.

Specific examples of ester monomers include crotonates such as ethyleneglycol di-crotonate, tetramethylene glycol di-crotonate, pentaerythritoldi-crotonate and sorbitol tetra-crotonate.

Specific examples of ester monomers include isocrotonates such asethylene glycol di-isocrotonate, pentaerythritol di-isocrotonate, andsorbitol tetra-isocrotonate.

Specific examples of ester monomers include maleates such as ethyleneglycol di-maleate, triethylene glycol di-maleate, pentaerythritoldi-maleate, and sorbitol tetra-maleate.

Examples of other ester monomers are esters of aliphatic alcohols suchas those disclosed in J.P. KOKOKU Nos. Sho 46-27926 and Sho 51-47334 andJ.P. KOKAI Sho 57-196231; ester monomers having aromatic skeletons suchas those disclosed in J.P. KOKAI Nos. Sho 59-5240, Sho 59-5241 and Hei2-226149; and ester monomers having amino groups such as those disclosedin J.P. KOKAI Hei 1-165613. Moreover, the foregoing ester monomers maybe used as a mixture.

In addition, examples of amide monomers of aliphatic polyvalent aminecompounds with unsaturated carboxylic acids includemethylene-bis-acrylamide, methylene-bis-methacrylamide,1,6-hexamethylene-bis-acrylamide, 1,6-hexamethylene-bis-methacrylamide,diethylene triamine tris-acrylamide, xylylene-bis-acrylamide, andxylylene-bis-methacrylamide. Examples of other amide type monomerspreferably used herein are those having cyclohexylene structures such asthose disclosed in J.P. KOKOKU Sho 54-21726.

Moreover, preferably used herein also include urethane type additionpolymerizable compounds prepared while making use of the additionreactions of isocyanates with compounds having hydroxyl groups andspecific examples thereof are vinyl urethane compounds having at leasttwo polymerizable vinyl groups in the molecule, which can be prepared byadding hydroxyl group-containing vinyl monomers represented by thefollowing general formula (A) to poly-isocyanate compounds carrying atleast two isocyanate groups in the molecule, such as those disclosed inJ.P. KOKOKU Sho 48-41708:CH₂═C(R₄)COOCH₂CH(R₅)—OH  (A)(In the Formula (A), each of R₄ and R₅ represents —H or —CH₃).

Suitably used herein likewise include, for instance, urethane acrylatessuch as those disclosed in J.P. KOKAI Sho 51-37193 and J.P. KOKOKU Nos.Hei 2-32293 and Hei 2-16765; and urethane compounds having ethyleneoxide type skeletons such as those disclosed in J.P. KOKOKU Nos. Sho58-49860, Sho 56-17654, Sho 62-39417 and Sho 62-39418. Furthermore, theuse of addition polymerizable compounds having amino and/or sulfidestructures in the molecule such as those disclosed in J.P. KOKAI Nos.Sho 63-277653, Sho 63-260909 and Hei 1-105238 would permit thepreparation of a photopolymerizable composition quite excellent in thephoto-polymerization speed.

Other examples of the foregoing monomers are multi-functional acrylatesand methacrylates such as polyester acrylates and epoxy acrylatesobtained by reacting epoxy resins with (meth)acrylic acids such as thosedisclosed in J.P. KOKAI Sho 48-64183 and J.P. KOKOKU Nos. Sho 49-43191and Sho 52-30490; specific unsaturated compounds such as those disclosedin J.P. KOKOKU Nos. Sho 46-43946, Hei 1-40337 and Hei 1-40336 and vinylphosphonic acid type compounds such as those disclosed in J.P. KOKAI Hei2-25493; monomers having structures containing perfluoro-alkyl groupssuch as those disclosed in J.P. KOKAI Sho 61-22048, which are suitablyused in some cases; and those introduced, as optically curable monomersor oligomers, in Bulletin of Adhesive Society of Japan, 1984, Vol. 20,No. 7, pp. 300–308.

Regarding these ethylenically unsaturated bond-containing monomers, thedetails concerning, for instance, the structures, the manner of use(independent use or use in combination), and the amount to be added canarbitrarily be determined or selected in the light of the ultimatequality design thereof. For instance, the details of the monomers may beselected on the basis of the following standpoints. Preferably used suchmonomers are those having a structure containing a large number ofunsaturated bonds in the molecule and in most of cases, preferably usedare those having at least two functional groups, from the viewpoint ofthe polymerization speed. Moreover, those having at least threefunctional groups are preferably used in case where it is desired toincrease the strength of the image area or the cured film and it is alsoeffective to combine these monomers in such a manner that they comprisethose having different numbers of functional groups and/or polymerizablegroups (such as acrylic acid esters, methacrylic acid esters, styrenetype compounds, vinyl ether type compounds), for the simultaneouscontrol of the both light-sensitivity and strength. Compounds havinghigh molecular weights and those having high hydrophobicity areeffective for the preparation of image-recording layer excellent in theboth polymerization speed and strength, but they suffer from problemssuch that the layer is insufficient in the developing speed and it isaccompanied by the formation of precipitates in the developer used.Further, the selection of addition polymerizable compounds and themanner of using the same are quite important in consideration of thecompatibility with other components in the composition (such as a binderpolymer, an initiator and a coloring agent) and the dispersibility ofthe same in the composition. In this respect, the compatibility maysometimes be improved by, for instance, the use of low purity compoundsor the simultaneous use of at least two compounds.

In addition, when applied to a lithographic printing plate precursor,the use of such a compound having a specific structure may be selectedin order to improve the adhesion of the image-recording layer to, forinstance, the substrate and an overcoat layer as will be describedbelow.

Regarding the rate of the ethylenically unsaturated bond-containingmonomer to be incorporated into the image-recording layer, the higherthe rate of the monomer, the higher the sensitivity of the resultinglayer, but if the rate is too high, various problems arise, forinstance, the resulting composition causes undesirable phase separation,various troubles possibly encountered in the production processes (suchas the production of rejects due to the transfer and adhesion of somecomponents of the image-recording layer) are caused due to thestickiness of the image-recording layer when applied to a lithographicprinting plate precursor and precipitates are formed in a developerduring development. From the foregoing standpoints, the amount of theethylenically unsaturated bond-containing monomer preferably ranges from5 to 80% by weight and more preferably 25 to 75% by weight on the basisof the weight of the non-volatile components present in the composition.Moreover, these monomers may be used alone or in any combination.Besides, the structure, mixing ratio and added amount of the monomer canarbitrarily and appropriately be selected while taking intoconsideration the magnitude of the polymerization-inhibitory effect withrespect to oxygen, resolution, fogging, refractive index changes andsurface stickiness. When forming an image-recording layer by applying acomposition for image-recording layers, the layer may have a layerstructure comprising an under coat and a top coat according to a methodfor forming such a layer structure.

(Binder Polymers)

The binder polymer incorporated into the image-recording layer used inthe invention is added to the composition for the purpose of improvingthe quality of the resulting film and may be a variety of polymersinasmuch as they have an effect of improving the quality of theresulting film. Binder polymers suitably used in the invention are thosehaving repeating units represented by the following general formula (i)among others:

The binder polymer having repeating units represented by the foregoinggeneral formula (i) will occasionally be referred to also as “specificbinder polymer” and will be described in detail below.

First, R¹ appearing in Formula (i) represents a hydrogen atom or amethyl group, with a methyl group being particularly preferred.

The connecting group represented by R² in Formula (i) is one constitutedby hydrogen, oxygen, nitrogen, sulfur and/or halogen atoms and having anumber of atoms except for those included in substituents ranging from 2to 30. Specific examples thereof are alkylene, substituted alkylene,arylene and substituted arylene groups. The connecting group may have astructure formed by coupling a plurality of the foregoing bivalentgroups through amide bonds and/or ester bonds.

Examples of connecting groups having chain structures are ethylene andpropylene groups. Examples of preferred connecting groups also includethose having structures obtained by connecting these alkylene groupsthrough ester bonds.

Among these connecting groups represented by R² in Formula (i),preferably used in the invention are hydrocarbon groups having a valencyof (n+1) and aliphatic ring structures each having 3 to 30 carbon atoms.Specific examples thereof are compounds having aliphatic ring structuressuch as cyclopropane, cyclopentane, cyclohexane, cycloheptane,cyclooctane, cyclodecane, di-cyclohexyl, ter-cyclohexyl, and norbornane,which may be substituted with at least one arbitrarily selectedsubstituent, whose hydrogen atoms (n+1) present on any carbon atomconstituting the compound are removed to thus form hydrocarbon groupseach having a valency of (n+1). R² preferably has 3 to 30 carbon atomsincluding those constituting the substituents.

At least one carbon atom of the compound constituting the aliphatic ringstructure may be replaced with a hetero atom selected from the groupconsisting of nitrogen, oxygen and sulfur atoms. When taking intoconsideration the printing durability of the resulting printing plate,R² is preferably a hydrocarbon group having a valency of (n+1) and asubstituted or unsubstituted aliphatic ring structure which has 3 to 30carbon atoms and includes at least two rings, such as a condensedpolycyclic aliphatic hydrocarbon, a crosslinked cyclic aliphatichydrocarbon, a spiro-aliphatic hydrocarbon or a collected aliphatichydrocarbon ring (an assembly obtained by connecting a plurality ofrings through bonds or connecting groups). In this case, the number ofcarbon atoms includes those present in the substituents.

Further, the connecting group represented by R² is preferably one having5 to 10 carbon atoms and is also preferably one having a chain structurecontaining ester bonds in the structure or one having a ring structuresuch as that described above, while taking into consideration thestructure thereof.

The substituents capable of being introduced into the connecting grouprepresented by R² may be non-metallic monovalent atomic groups exceptfor hydrogen atom. Specific examples thereof are halogen atoms (—F, —Br,—Cl, —I), hydroxyl group, alkoxy groups, aryloxy groups, mercaptogroups, alkyl-thio groups, aryl-thio groups, alkyl-dithio groups,aryl-dithio groups, amino groups, N-alkylamino groups, N,N-dialkyl-aminogroups, N-arylamino groups, N,N-diaryl-amino groups, N-alkyl-N-arylaminogroups, acyloxy groups, carbamoyloxy groups, N-alkyl-carbamoyloxygroups, N-aryl-carbamoyloxy groups, N,N-dialkyl-carbamoyloxy groups,N,N-diaryl-carbamoyl-oxy groups, N-alkyl-N-aryl-carbamoyloxy groups,alkyl-sulfoxy groups, aryl-sulfoxy groups, acylthio groups, acylaminogroups, N-alkyl-acylamino groups, N-aryl-acyl-amino groups, ureidogroup, N′-alkyl-ureido groups, N′,N′-dialkyl-ureido groups,N′-aryl-ureido groups, N′,N′-diaryl-ureido groups,N′-alkyl-N′-aryl-ureido groups, N-alkyl-ureido groups, N-aryl-ureidogroups, N′-alkyl-N-alkyl-ureido groups, N′-alkyl-N-aryl-ureido groups,N′,N′-dialkyl-N-alkyl-ureido groups, N′,N′-dialkyl-N-aryl-ureido groups,N′-alkyl-N-aryl-ureido groups, N′-aryl-N-alkyl-ureido groups,N′-aryl-N-aryl-ureido groups, N′,N′-diaryl-N-alkyl-ureido groups,N′,N′-diaryl-N-aryl-ureido groups, N′-alkyl-N′-aryl-N-alkyl-ureidogroups, N′-alkyl-N′-aryl-N-aryl-ureido groups, alkoxy-carbonylaminogroups, aryloxy-carbonylamino groups, N-alkyl-N-alkoxy-carbonylaminogroups, N-alkyl-N-aryloxy-carbonylamino groups,N-aryl-N-alkoxy-carbonylamino groups, N-aryl-N-aryloxy-carbonylaminogroups, N-aryl-N-carbonylamino groups, formyl group, acyl groups,carboxyl groups and conjugated base groups thereof, alkoxy-carbonylgroups, aryloxy-carbonyl groups, carbamoyl groups, N-alkyl-carbamoylgroups, N,N-dialkyl-carbamoyl groups, N-aryl-carbamoyl groups,N,N-diaryl-carbamoyl groups, N-alkyl-N-aryl-carbamoyl groups,alkyl-sulfinyl groups, aryl-sulfinyl groups, alkyl-sulfonyl groups,aryl-sulfonyl groups, sulfo group (—SO₃H) and conjugated base groupsthereof, alkoxy-sulfonyl groups, aryloxy-sulfonyl groups, sulfinamoylgroups, N-alkyl-sulfinamoyl groups, N,N-dialkyl-sulfinamoyl groups,N-aryl-sulfinamoyl groups, N,N-diaryl-sulfinamoyl groups,N-alkyl-N-aryl-sulfinamoyl groups, sulfamoyl groups, N-alkyl-sulfamoylgroups, N,N-dialkyl-sulfamoyl groups, N-aryl-sulfamoyl groups,N,N-diaryl-sulfamoyl groups, N-alkyl-N-aryl-sulfamoyl groups,N-acyl-sulfamoyl groups and conjugated base groups thereof,N-alkylsulfonyl-sulfamoyl groups (—SO₂NHSO₂(alkyl)) and groups derivedfrom conjugated bases thereof, N-arylsulfonyl-sulfamoyl groups(—SO₂NHSO₂(aryl)) and groups derived from conjugated bases thereof,N-alkylsulfonyl-carbamoyl groups (—CONHSO₂(alkyl)) and groups derivedfrom conjugated bases thereof, N-arylsulfonyl-carbamoyl groups(—CO—NHSO₂(aryl)) and groups derived from conjugated bases thereof,alkoxy-silyl groups (—Si(O-alkyl)₃), aryloxy-silyl groups(—Si(O-aryl)₃), hydroxy-silyl groups (—Si(OH)₃) and groups derived fromconjugated bases thereof, phosphono groups (—PO₃H₂) and groups derivedfrom conjugated bases thereof, dialkyl-phosphono groups (—PO₃(alkyl)₂),diaryl-phosphono groups (—PO₃(aryl)₂), alkylaryl-phosphono groups(—PO₃(alkyl)(aryl)), mono-alkyl-phosphono groups (—PO₃H(alkyl)) andgroups derived from conjugated bases thereof, monoaryl-phosphono groups(—PO₃H(aryl)) and groups derived from conjugated bases thereof,phosphono-oxy groups (—OPO₃H₂) and groups derived from conjugated basesthereof, dialkyl-phosphono-oxy groups (—OPO₃(alkyl)₂),diaryl-phosphono-oxy groups (—OPO₃(aryl)₂), alkylaryl-phosphono-oxygroups (—OPO₃(alkyl)(aryl)), monoalkyl-phosphono-oxy groups(—OPO₃H(alkyl)) and groups derived from conjugated bases thereof,monoaryl-phosphono-oxy groups (—OPO₃H(aryl)) and groups derived fromconjugated bases thereof, cyano group, nitro group, dialkyl-boryl groups(—B(alkyl)₂), diaryl-boryl groups (—B(aryl)₂), alkylaryl-boryl groups(—B(alkyl)(aryl)), di-hydroxy-boryl group (—B(OH)₂) and groups derivedfrom conjugated bases thereof, alkylhydroxy-boryl groups (—B(alkyl)(OH))and groups derived from conjugated bases thereof, arylhydroxy-borylgroups (—B(aryl)(OH)) and groups derived from conjugated bases thereof,aryl groups, alkenyl groups and alkynyl groups.

In the image-forming material used in the invention, substituents havinghydrogen atoms capable of forming hydrogen bonds and, in particular,those having such an acidity that the acid dissociation constant (pKa)thereof is smaller than that of the carboxylic acid are not preferablyused since they have a tendency of reducing the printing durability ofthe resulting printing plate, although this is dependent on the designof the image-recording layer. On the other hand, the use of halogenatoms and hydrophobic substituents such as hydrocarbon groups (such asalkyl, aryl, alkenyl and alkynyl groups), alkoxy groups and aryloxygroups is preferred since they have a tendency of improving the printingdurability of the resulting printing plate and, in particular, when thering structure is a 6-membered or lower mono-cyclic aliphatichydrocarbon such as cyclopentane or cyclohexane, the binder polymerspreferably have such hydrophobic substituents. These substituents may,if possible, form a ring between them or through the formation oflinkages with the hydrocarbon group to which they are bonded or thesubstituents may further have substituents.

When A in Formula (i) is NR³—, R³ represents a hydrogen atom or amonovalent hydrocarbon group having 1 to 10 carbon atoms. Examples ofsuch monovalent hydrocarbon group having 1 to 10 carbon atomsrepresented by R³ are alkyl, aryl, alkenyl and alkynyl groups.

Specific examples of alkyl groups are linear, branched or cyclic alkylgroups having 1 to 10 carbon atoms such as methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl,sec-butyl, tert-butyl, isopentyl, neopentyl, 1-methylbutyl, isohexyl,2-ethylhexyl, 2-methylhexyl, cyclopentyl, cyclohexyl, 1-adamantyl and2-norbornyl groups.

Specific examples of aryl groups are aryl groups having 6 to 10 carbonatoms such as phenyl, naphthyl and indenyl groups; and hetero-arylgroups containing a hetero atom selected from the group consisting ofnitrogen, oxygen and sulfur atoms and having 6 to 10 carbon atoms suchas furyl, thienyl, pyrrolyl, pyridyl, quinolyl groups.

Specific examples of alkenyl groups are linear, branched or cyclicalkenyl groups having 2 to 10 carbon atoms such as vinyl, 1-propenyl,1-butenyl, 1-methyl-1-propenyl, 1-cyclopentenyl and 1-cyclohexenylgroups.

Specific examples of alkynyl groups are those having 2 to 10 carbonatoms such as ethynyl, 1-propynyl, 1-butynyl and 1-octynyl groups. Thesubstituents which may be introduced into R³ are the same as thoselisted above in connection with the substituents capable of beingintroduced into R². In this respect, however, the number of carbon atomsof R³ ranges from 1 to 10 including that present in the substituent.

The symbol A appearing in Formula (i) is preferably an oxygen atom or—NH— since such a compound can easily be prepared.

In Formula (i), n is an integer ranging from 1 to 5 and preferably 1from the viewpoint of the printing durability of the resulting printingplate.

The following are specific examples of preferred repeating unitsrepresented by Formula (i), but the present invention is not restrictedto these specific examples at all.

The binder polymer may comprise only one or at least two kinds ofrepeated units represented by Formula (i). Specific binder polymers usedin the present invention may comprise only the repeating unitsrepresented by Formula (i), but they are in general in the form ofcopolymers of the foregoing repeating units with units derived fromother copolymerizable components. The total content of the repeatingunits represented by Formula (i) in the copolymer is properly determinedwhile taking into consideration, for instance, the structure of thecopolymer and the design of the composition, but the content preferablyranges from 1 to 99 mole %, more preferably 5 to 40 mole % and furtherpreferably 5 to 20 mole % on the basis of the total molar amount of thepolymer component.

When the binder polymer used is in the form of a copolymer, thecopolymerizable components are not particularly restricted to specificones and may be any conventionally known one inasmuch as they areradical-polymerizable monomers. Specific examples thereof are monomersdisclosed in “Data Handbook of Polymer, Fundamentals, edited by PolymerSociety of Japan, published by Baifukan, 1986”. The copolymerizablecomponents may be used alone or in any combination of at least two ofthem.

The molecular weight of the specific binder polymer used in theinvention is appropriately selected in consideration of theimage-forming ability of the resulting composition and the printingdurability of the resulting lithographic printing plate precursor. Ingeneral, the higher the molecular weight of the polymer, the higher theprinting durability of the precursor, but the image-forming ability isliable to be deteriorated. Contrary to this, the lower the molecularweight of the polymer, the better the image-forming ability, but theprinting durability is reduced. Accordingly, the molecular weight of thepolymer preferably ranges from 2,000 to 1,000,000, more preferably 5,000to 500,000 and further preferably 10,000 to 200,000.

The binder polymer used in the invention may comprise such a specificbinder polymer alone, but may be a mixture thereof with at least onebinder polymer other than the specific one. The content of the binderpolymer used simultaneously with the specific one ranges from 1 to 60%by weight, preferably 1 to 40% by weight and further preferably 1 to 20%by weight on the basis of the total weight of the binder polymercomponent. The binder polymers which can be used simultaneously with thespecific one may be any conventionally known one without any restrictionand specific examples thereof preferably used herein are binders havingacrylic main chains and urethane binders currently used in this field.

The total amount of the specific binder polymer and the additionalbinder polymer in the composition may properly be selected, but it ingeneral ranges from 10 to 90% by weight, preferably 20 to 80% by weightand more preferably 30 to 70% by weight on the basis of the total weightof the non-volatile components present in the composition.

The acid value (meq/g) of such a binder polymer preferably ranges from2.00 to 3.60.

<Other Binder Polymers Simultaneously Used Herein>

The other binder polymers capable of being used simultaneously with thespecific binder polymers are preferably radical polymerizablegroup-containing binder polymers. Such a radical polymerizable group isnot restricted to specific ones inasmuch as they can be subjected to theradical polymerization, but specific examples thereof includeα-substituted methyl acrylate group [—OC(═O)—C(—CH₂Z)═CH₂, wherein Zrepresents a hydrocarbon group starting from a hetero atom], acryl,methacryl, allyl and styryl group, with acryl and methacryl groups beingpreferably used herein.

The amount of the radical polymerizable groups present in the binderpolymer (the content of radical polymerizable unsaturated double bondsas determined by the iodometry) preferably ranges from 0.1 to 10.0 mM,more preferably 1.0 to 7.0 mM and most preferably 2.0 to 5.5 mM per unitamount (1 g) of the binder polymer. If the content thereof is lower than0.1 mM, the resulting composition sometimes shows an insufficient curingability and the sensitivity thereof is accordingly low. On the otherhand, if it exceeds 10.0 mM, the resulting composition often becomesunstable and the storage stability thereof is, in turn, reduced.

Further, the other binder polymers simultaneously used preferably has analkali-soluble group. The content (the acid value as determined by theneutralization titration) of the alkali-soluble group in the binderpolymer preferably ranges from 0.1 to 3.0 mM, more preferably 0.2 to 2.0mM and most preferably 0.45 to 1.0 mM per unit amount (1 g) of thebinder polymer. If the content thereof is less than 0.1 mM, the binderpolymer may often be precipitated in the developer during development tothus generate scum in the developer, while if it exceeds 3.0 mM, thehydrophilicity of the binder polymer is too high and when applied to alithographic printing plate precursor, the printing durability of theresulting printing plate is sometimes reduced.

The weight average molecular weight of such a binder polymer preferablyranges from 2,000 to 1,000,000, more preferably 10,000 to 300,000 andmost preferably 20,000 to 200,000. If the weight average molecularweight thereof is lower than 2,000, the film-forming ability of theresulting composition is often reduced and this in turn results in theformation of a printing plate having insufficient printing durability,while if it exceeds 1,000,000, the polymer is sometimes hardly solublein a solvent for coating and the composition accordingly hasinsufficient coating properties.

In addition, the glass transition point (Tg) of such a binder polymerpreferably falls within the range of from 70 to 300° C., more preferably80 to 250° C. and most preferably 90 to 200° C. If the glass transitionpoint thereof is less than 70° C., the resulting composition sometimeshas insufficient storage stability and when applied to a lithographicprinting plate precursor, the printing durability of the resultingprinting plate is correspondingly reduced, while if it exceeds 300° C.,the resulting composition sometimes has a low sensitivity because of thereduction in the radical mobility in the composition.

To make the glass transition point of the binder polymer higher, it ispreferred to incorporate amide groups and/or imide groups, inparticular, those derived from methacrylamide-methacrylamide derivativesinto the binder molecule.

The image-recording layer used in the invention may further comprise, inaddition to the foregoing essential components, other componentssuitably used depending on the applications thereof and the methods forproducing the same according to need. Such additives preferably usedherein will be described or exemplified below.

(Polymerization Inhibitors)

It is desirable in the present invention to add a small amount of a heatpolymerization inhibitor to the image-forming composition for theinhibition of unnecessary heat polymerization of the polymerizableethylenically unsaturated double bond-containing compound or theethylenically unsaturated bond-containing monomer. Examples of heatpolymerization inhibitors appropriately used herein are hydroquinone,p-methoxy phenol, di-t-butyl-p-cresol, pyrogallol, t-butyl catechol,benzoquinone, 4,4′-thiobis(3-methyl-6-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol) and N-nitrosophenylhydroxylamine cerous salt. The amount of the heat polymerizationinhibitory agent to be added to the composition preferably ranges fromabout 0.01% by weight to about 5% by weight based on the weight of thenon-volatile components present in the composition. Moreover, a higherfatty acid or a derivative thereof such as behenic acid or behenic acidamide can, for instance, be added to the composition to eliminate anypolymerization-inhibitory effect of oxygen. Thus, the derivative or thelike can locally be distributed in the surface region of the resultingimage-recording layer by the action of the drying step after theapplication of the composition. The amount of the higher fatty acidderivative to be incorporated into the composition preferably rangesfrom about 0.5% by weight to about 10% by weight on the basis of theweight of the non-volatile components present in the composition.

(Coloring Agents)

The image-forming material used in the invention may further comprise adye or a pigment for the coloration of the material. If the material isused for making a printing plate, the so-called plate-examiningproperties such as the visibility after the plate-making operations andthe image density determination properties of the resulting plate can beimproved. When using a dye as a coloring agent, the photopolymerizableimage-recording layer frequently shows reduction of sensitivity in mostof cases and therefore, a pigment is preferably used as a coloringagent. Specific examples of such coloring agents are pigments such asphthalocyanine pigments, azo pigments, carbon black and titanium oxide;and dyes such as Ethyl Violet, Crystal Violet, azo dyes, anthraquinonedyes and cyanine dyes. The amount of these dyes or pigments as coloringagents to be incorporated into the composition for forming theimage-recording layer preferably ranges from about 0.5% by weight toabout 5% by weight on the basis of the weight of the non-volatilecomponents present in the composition.

(Other Additives)

Moreover, the image-forming material may optionally comprise knownadditives such as an inorganic filler for improving physical propertiesof the resulting cured film, other plasticizers and a sensitizing agent(ink-receptivity improver) which can improve the ink-receptivity of thesurface of the image-recording layer. Examples of such plasticizers aredioctyl phthalate, didodecyl phthalate, triethylene glycol di-caprylate,dimethyl glycol phthalate, tricresyl phosphate, dioctyl adipate, dibutylsebacate, and triacetyl glycerin. The plasticizer may be added to thecomposition usually in an amount of not more than 10% by weight on thebasis of the sum of the binder polymer and the ethylenically unsaturatedbond-containing monomer. Moreover, in the lithographic printing plateprecursor as will be detailed below, it is also possible to add, to thecomposition, a UV initiator and a thermal crosslinking agent forenhancing the effects of heating and/or light-exposure steps carried outafter the development or for the improvement of the film strength(printing durability).

The foregoing composition can suitably be used for forming theimage-recording layer of the image-forming material used in theinvention as will be detailed below.

[Image-Forming Material]

The image-forming material used in the invention is one comprising asubstrate provided thereon with an image-recording layer. The materialmay optionally comprise a protective layer on the image-recording layer.The image-recording layer comprises the components described above indetail. Such an image-forming material can be prepared by dissolving, ina solvent, components required for preparing a coating liquid forforming an image-recording layer or components required for preparing acoating liquid for forming a desired layer such as a protective layerand then applying these coating liquids onto an appropriate substrate oran intermediate layer.

[Image-Recording Layer]

The image-recording layer used in the invention is a heat-polymerizablenegative-working image-recording layer comprising an infrared absorber,a polymerization initiator, an ethylenically unsaturated bond-containingmonomer (also referred to as addition-polymerizable compound) and abinder polymer. The image-forming mechanism of such a heat-polymerizablenegative-working image-recording layer is as follows: the polymerizationinitiator is decomposed by the action of heat to thus generate radicalsand the radicals thus generated induce the polymerization reaction ofthe ethylenically unsaturated bond-containing monomer. Moreover, thelithographic printing plate precursor as an image-forming material usedin the invention is particularly suitable for use in the directplate-making method which makes use of laser rays having a wavelengthranging from 760 to 1,200 nm and it would show printing durability andan image-forming ability superior to those observed for the conventionallithographic printing plate precursor.

The foregoing image-recording layer is formed by dissolving thecomposition comprising the foregoing components for forming theimage-recording layer of the invention in a variety of organic solventsand then applying the resulting solution onto a substrate or anintermediate layer. Examples of such solvents used herein are acetone,methyl ethyl ketone, cyclohexane, ethyl acetate, ethylene dichloride,tetrahydrofuran, toluene, ethylene glycol monomethyl ether, ethyleneglycol mono-ethyl ether, ethylene glycol dimethyl ether, propyleneglycol monomethyl ether, propylene glycol mono-ethyl ether,acetyl-acetone, cyclohexanone, diacetone alcohol, ethylene glycolmonomethyl ether acetate, ethylene glycol ethyl ether acetate, ethyleneglycol mono-isopropyl ether, ethylene glycol mono-butyl ether acetate,3-methoxypropanol, methoxy-methoxy ethanol, diethylene glycol monomethylether, diethylene glycol mono-ethyl ether, diethylene glycol dimethylether, diethylene glycol diethyl ether, propylene glycol monomethylether acetate, propylene glycol monoethyl ether acetate,3-methoxy-propyl acetate, N,N-dimethylformamide, dimethylsulfoxide,γ-butyrolactone, methyl lactate and ethyl lactate. These solvents may beused alone or in combination. The concentration of the solid contents inthe coating solution suitably ranges from 2 to 50% by weight.

The coated amount of the image-recording layer may mainly have effectsupon the sensitivity and developing ability of the image-recordinglayer, and the strength and printing durability of the exposed film andaccordingly, it is desirably selected depending on the applications. Inthis respect, if the coated amount is too small, the exposed film hasinsufficient printing durability, while if it is too large, thesensitivity of the resulting layer is reduced, it takes a long period oftime for the exposure and the development likewise requires a longperiod of time. Regarding the scanning exposure type lithographicprinting plate precursor concerning the principal object of theinvention, the coated amount thereof desirably ranges from about 0.1g/m² to about 10 g/m² as expressed in terms of the amount thereofdetermined after drying. More preferably, it ranges from 0.5 g/m² to 5g/m².

[Substrate]

As the substrate for the image-forming material used in the invention,the substrates conventionally known as hydrophilic substrates currentlyused in, for instance, the lithographic printing plate precursors may beused without any particular restriction.

The substrate used herein is preferably a plate-like substance havinggood dimensional stability and examples thereof include paper; paperlaminated with plastic films (such as polyethylene, polypropylene andpolystyrene films); metal plates (such as aluminum, zinc and copperplates); plastic films (such as cellulose diacetate, cellulosetriacetate, cellulose propionate, cellulose butyrate, cellulose acetatebutyrate, cellulose nitrate, polyethylene terephthalate, polyethylene,polystyrene, polypropylene, polycarbonate, and polyvinyl acetal films);and paper and plastic films which are laminated with the foils of theforegoing metals or on which the foregoing metals are deposited. Thesesubstrates may, if necessary, be subjected to appropriate known physicaland/or chemical surface treatments for the purposes of, for instance,imparting hydrophilicity to the surface and/or improving the strengththereof.

Examples of substrates particularly preferably used herein are paper, apolyester film and an aluminum plate. Among them, the aluminum plate mayfurther preferably be used since it is excellent in the dimensionalstability, it is relatively cheap and those excellent in thehydrophilicity and strength can easily be obtained by desired surfacetreatments. Examples of substrates likewise preferably used hereininclude composite sheets each comprising a polyethylene terephthalatefilm and an aluminum sheet adhered thereto such as those disclosed inJ.P. KOKOKU Sho 48-18327.

The aluminum plate used herein means a metal plate comprisingdimensionally stable aluminum as a principal component and the plate canbe selected from the group consisting of a pure aluminum plate, a plateof an alloy comprising aluminum as a main component and trace amounts offoreign elements, and a plastic film or paper which comprises analuminum (or an alloy thereof) foil or layer laminated with or depositedon the same. In the following description, the foregoing substratesconsisting of aluminum or aluminum alloys are hereunder genericallyreferred to as “aluminum substrate(s)”. The foreign elements included inthe foregoing aluminum alloys are, for instance, silicon, iron,manganese, copper, magnesium, chromium, zinc, bismuth, nickel andtitanium and the total content of these foreign elements in the alloy isnot more than 10% by weight. In the present invention, the use of a purealuminum substrate is preferred, but aluminum substrates each containinga trace amount of foreign elements may likewise suitably be used hereinsince it is difficult to produce completely pure aluminum due to thelimit of the refining technique. Thus, the aluminum plate used in thepresent invention is not limited in its composition and usable hereininclude, for instance, those prepared from conventionally known andcurrently used materials such as JIS A 1050, JIS A 1100, JIS A 3103 andJIS A 3005.

The thickness of the aluminum substrate used in the invention is on theorder of about 0.1 to 0.6 mm. The thickness can arbitrarily be changeddepending on the size of a printing press used, the size of the finallyprepared printing plate and the requirements of users. The aluminumsubstrate may if necessary be subjected to the followingsurface-treatments. It is a matter of course that thesesurface-treatments are not essential in the present invention.

(Surface-Roughening Treatment)

When using a surface-roughened substrate, examples of suchsurface-roughening treatments are mechanical surface-roughening,chemical etching and electrolytic graining treatments such as thosedisclosed in J.P. KOKAI Sho 56-28893. Examples of surface-rougheningtreatments usable herein also include an electrochemicalsurface-roughening treatment wherein an aluminum substrate iselectrochemically surface-roughened in an electrolyte such as ahydrochloric acid or nitric acid solution; and mechanicalsurface-roughening methods such as a wire brush-graining method in whichthe aluminum surface is scratched with metal wires, a ball grainingmethod in which the aluminum surface is grained with abrasive spheresand an abrasive and a brush graining method wherein the aluminum surfaceis roughened using a nylon brush and an abrasive. The foregoingsurface-roughening methods can be used alone or in any combination.Among them, preferably used herein is the electrochemicalsurface-roughening treatment wherein an aluminum substrate iselectrochemically surface-roughened in a hydrochloric acid or nitricacid solution as an electrolyte and in this case, a suitable anode timeelectricity is in the range of from 50 to 400 C/dm². More specifically,an aluminum substrate is subjected to alternating and/or direct currentelectrolyzation carried out in an electrolyte containing 0.1 to 50%hydrochloric acid or nitric acid under the following conditions: atemperature ranging from 20 to 80° C.; an electrolyzation time rangingfrom one second to 30 minutes; and a current density ranging from 100 to400 C/dm².

The aluminum substrate thus surface-roughened may be chemically etchedwith an acid or an alkali. Examples of etching agents suitably usedherein are sodium hydroxide, sodium carbonate, sodium aluminate, sodiummeta-silicate, sodium phosphate, potassium hydroxide and lithiumhydroxide and the preferred concentration of such an etching agent andthe preferred etching temperature range from 1 to 50% and 20 to 100° C.,respectively. The aluminum substrate is then washed with an acid for theremoval of contaminants (smut) remaining on the surface after theetching treatment. Acids usable herein are, for instance, nitric acid,sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid,borofluoric acid. Particularly preferred methods for removing smut afterthe electrochemical surface-roughening treatment include, for instance,a method comprising bringing the aluminum substrate into contact with a15 to 65% by weight sulfuric acid solution maintained at a temperatureranging from 50 to 90° C. disclosed in J.P. KOKAI Sho 53-12739 and amethod comprising etching the aluminum substrate with an alkalidisclosed in J.P. KOKOKU Sho 48-28123. The methods and conditions ofthese treatments are not particularly restricted to specific onesinasmuch as the central line-average surface roughness Ra falls withinthe range of from 0.2 to 0.5 μm after the foregoing treatments of thesubstrate.

(Anodization Treatment)

The aluminum substrate on which an oxide layer is formed by theforegoing treatments may further be subjected to anodization, ifnecessary. The anodization treatment employs an aqueous solution ofsulfuric acid, phosphoric acid, oxalic acid or boric acid/sodium borateor any combination of a plurality thereof as a principal component ofthe electrolytic bath. In this respect, the electrolyte may of coursecomprise components usually included in, for instance, at least an Alalloy plate, electrodes, tap water and underground water. Moreover, itmay further comprise second and third components. The term “second andthird components” herein used means, for instance, metal ions such asNa, K, Mg, Li, Ca, Ti, Al, V, Cr, Mn, Fe, Co, Ni, Cu and Zn ions;cations such as ammonium ions; and anions such as nitrate ions,carbonate ions, chloride ions, phosphate ions, fluoride ions, sulfiteions, titanate ions, silicate ions and borate ions and the concentrationthereof ranges from about 0 to 10000 ppm. The conditions for theanodization are not particularly restricted, but the aluminum substrateis treated according to the alternating or direct currentelectrolyzation carried out at an electrolyte concentration ranging from30 to 500 g/L; an electrolyte temperature ranging from 10 to 70° C.; anda current density ranging from 0.1 to 40 A/m². The thickness of theanodized layer thus formed ranges from 0.5 to 1.5 μm and preferably 0.5to 1.0 μm. The conditions for the anodization treatment canappropriately be selected in such a manner that the substrate hasmicropores in the anodized layer thereof and that the pore size and poredensity fall within the ranges of from 5 to 10 nm and 8×10¹⁵ to2×10¹⁶/m², respectively.

The surface of the foregoing substrate may be hydrophilized by a widevariety of known methods. A particularly preferred hydrophilizationtreatment is carried out using, for instance, a silicate or a polyvinylphosphonic acid. The hydrophilization layer is formed in an amountranging from 2 to 40 mg/m² and more preferably 4 to 30 mg/m² asexpressed in terms of the amount of Si or P element. The amount of thelayer can be determined by the fluorescent X-ray analysis.

More specifically, the foregoing hydrophilization treatment is carriedout by immersing the aluminum substrate, on which an anodized layer isformed, in an aqueous solution containing 1 to 30% by weight, preferably2 to 15% by weight of an alkali metal silicate or a polyvinyl phosphonicacid and having a pH as determined at 25° C. ranging from 10 to 13, forinstance, at a temperature ranging from 15 to 80° C. for 0.5 to 120seconds.

The alkali metal silicate used in the foregoing hydrophilizationtreatment may be, for instance, sodium silicate, potassium silicate andlithium silicate. Examples of hydroxides used for controlling the pHvalue of the aqueous alkali metal silicate solution are sodiumhydroxide, potassium hydroxide and lithium hydroxide. In this respect,the foregoing treating solution may additionally comprise an alkalineearth metal salt or a salt of a Group IVB metal. Examples of suchalkaline earth metal salts are nitrates such as calcium nitrate,strontium nitrate, magnesium nitrate and barium nitrate; andwater-soluble salts such as sulfates, chlorides, phosphates, acetates,oxalates and borates. Examples of salts of Group IVB metals are titaniumtetrachloride, titanium tri-chloride, potassium titanium fluoride,potassium titanium oxalate, titanium sulfate, titanium tetra-iodide,zirconium oxychloride, zirconium dioxide, zirconium oxychloride andzirconium tetrachloride.

The alkaline earth metal salts and salts of Group IVB metals may be usedalone or in any combination of at least two of them and the amount ofthese metal salts used in the treating solution preferably ranges from0.01 to 10% by weight and more preferably 0.05 to 5.0% by weight.Moreover, it is also effective to use the silicate electrodeposition asdisclosed in U.S. Pat. No. 3,658,662. It is likewise effective tocombine the electrolytically grained substrate disclosed in J.P. KOKOKUSho 46-27481 and J.P. KOKAI Nos. Sho 52-58602 and Sho 52-30503 with thecombination comprising the foregoing anodization and hydrophilizationtreatments.

In addition, the image-forming material used in the invention mayadditionally comprise an intermediate layer between the substrate andthe image-recording layer in order to improve the adhesion between themand the resistance to staining thereof Specific examples of suchintermediate layers suitably used herein are those disclosed in thefollowing publications: J.P. KOKOKU Sho 50-7481; J.P. KOKAI Nos. Sho54-72104, Sho 59-101651, Sho 60-149491, Sho 60-232998, Hei 3-56177, Hei4-282637, Hei 5-16558, Hei 5-246171, Hei 7-159983, Hei 7-314937, Hei8-202025, Hei 8-320551, Hei 9-34104, Hei 9-236911, Hei 9-269593, Hei10-69092, Hei 10-115931, Hei 10-161317, Hei 10-260536, Hei 10-282682,Hei 11-84674, Hei 11-38635, Hei 11-38629, Hei 10-282645, Hei 10-301262,Hei 11-24277, Hei 11-109641, Hei 10-319600, Hei 11-84674, Hei 11-327152,2000-10292, 2000-235254, 2000-352824, 2001-175001 and 2001-209170.

[Protective Layer (Overcoat Layer)]

In the present invention, a protective layer may be formed on theimage-recording layer. The protective layer is fundamentally formed toprotect the image-recording layer, but it also plays a role of an oxygenbarrier layer when the image-forming mechanism of the image-recordinglayer includes radical polymerization as in the present invention, andthe protective layer likewise serves as an ablation-inhibitory layerwhen the image-recording layer is exposed to an infrared laser beamhaving a high luminous intensity.

In addition to the foregoing characteristics, the protective layershould desirably satisfy the following requirements: it should neverinhibit the substantial transmission of the light rays used for theexposure; it should be excellent in the adhesion to the image-recordinglayer; and it can easily be removed in the developing step after theexposure. Regarding such an intermediate layer, there have variouslybeen devised and the details thereof are disclosed in U.S. Pat. No.3,458,311 and J.P. KOKOKU Sho 55-49729.

Materials preferably used for preparing such an intermediate layer are,for instance, water-soluble polymeric compounds relatively excellent inthe crystallinity and specific examples thereof are water-solublepolymers such as polyvinyl alcohol, vinyl alcohol-vinyl phthalatecopolymer, vinyl acetate-vinyl alcohol-vinyl phthalate copolymer, vinylacetate-crotonic acid copolymer, polyvinyl pyrrolidone, acidiccelluloses, gelatin, gum Arabic, poly(acrylic acid) andpoly(acrylamide), which may be used alone or in any combination. The useof polyvinyl alcohol as a principal component, among others, wouldprovide best results concerning the fundamental characteristics such asthe oxygen barrier properties and the ability of being easily removedduring development.

The polyvinyl alcohol used in the protective layer may be partiallyreplaced with esters, ethers and acetals inasmuch as it comprisesunsubstituted vinyl alcohol units required for imparting the desiredoxygen-barrier properties and water-solubility to the protective layer.In addition, it may likewise partially comprise other copolymerizablecomponents.

Examples of such polyvinyl alcohols are those which are hydrolyzed in arate of 71 to 100% and whose number of polymerized repeating units fallswithin the range of from 300 to 2400. Specific examples thereof arethose available from Kuraray Co., Ltd. such as PVA-105, PVA-110,PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HC,PVA-203, PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224,PVA-217EE, PVA-217E, PVA-220E, PVA-224E, PVA-405, PVA-420, PVA-613 andL-8.

The components of the protective layer (such as the selection of PVA,and the use of additives), the coated amount thereof or the like can beselected while taking into consideration a variety of requirements suchas the desired oxygen-barrier properties and the ability of the layer tobe removed during development as well as the fogging properties,adhesion properties and resistance to scratches. Generally, the higherthe rate of PVA-hydrolyzation (the higher the content of theunsubstituted vinyl alcohol units present in the oxygen-barrier layer)and the greater the thickness of the protective layer, the higher theresulting oxygen-barrier properties and accordingly, this isadvantageous to the sensitivity of the resulting image-recordingmaterial. However, if the oxygen-barrier properties are extremelyincreased, various problems arise such that the resultingimage-recording material may sometimes undergo an unnecessarypolymerization reaction during its preparation or the storage thereof inits green state (or in the un-exposed condition) and that there areobserved unnecessary fogging and thickening of printing images upon theimagewise exposure of the material.

For this reason, the oxygen permeability A of the protective layer asdetermined at 25° C. and 1 atm preferably falls within the followingrange: 0.2≦A≦20 (cc/m²·day).

The molecular weight of the (co)polymer such as the foregoing polyvinylalcohol (PVA) usable herein desirably ranges from 2000 to 10,000,000 andpreferably 20,000 to 3,000,000.

The composition for preparing such a protective layer may likewisecomprise, in addition to the foregoing components, for instance,glycerin or di-propylene glycol in an amount of several percents byweight based on the weight of the (co)polymer to thus impart flexibilityto the resulting protective layer. Alternatively, the composition mayalso comprise an anionic surfactant such as sodium alkyl-sulfate andsodium alkyl-sulfonate; an amphoteric surfactant such as a salt ofalkylamino-carboxylic acid or alkylamino-dicarboxylic acid; or anonionic surfactant such as polyoxyethylene alkylphenyl ether in anamount of several percents by weight based on the weight of the(co)polymer.

The thickness of the protective layer suitably ranges from 0.5 to 5 μmand, in particular, 0.5 to 2 μm.

Moreover, the characteristics of the protective layer such as adhesionproperties and resistance to scratches are likewise quite important inthe handling of the image-forming plate. More specifically, when ahydrophilic layer consisting of a water-soluble polymer is formed on alipophilic polymerizable layer, the former is liable to undergo peelingoff because of insufficient adhesion between them and defects such asinsufficient curing of the film are caused due to thepolymerization-inhibitory effect of oxygen within the area from whichthe hydrophilic layer has been peeled off. For this end, there have beenproposed a variety of techniques to improve the adhesion between thesetwo layers. For instance, U.S. patent application Ser. Nos. 292,501 and44,563 disclose that the desired satisfactory adhesion between these twolayers can be ensured by incorporating an acrylic emulsion or awater-insoluble vinyl pyrrolidone-vinyl acetate copolymer into ahydrophilic polymer mainly comprising a polyvinyl alcohol in an amountranging from 20 to 60% by weight and then applying the resulting mixtureonto the polymerizable layer. All of these known techniques can beapplied to the protective layer used in the present invention. Such amethod for coating a protective layer is disclosed in, for instance,U.S. Pat. No. 3,458,311 and J.P. KOKOKU Sho 55-49729.

The image-forming method of the invention includes an imagewise exposurestep and a developing step of the image-recording layer.

An infrared laser may be a light source suitably used in the inventionfor exposing the image-recording layer and images can likewise thermallybe recorded on the image-recording layer using a UV lamp or a thermalhead.

Among these, it is preferred in the invention that the image-recordinglayer is imagewise exposed to light using a solid state laser or asemiconductor laser emitting infrared rays whose wavelengths fall withinthe range of from 750 to 1400 nm. The output of the laser is preferablynot less than 100 mW and it is also preferred to use a multi-beam laserdevice in order to shorten the exposure time. Moreover, the exposuretime per picture element is preferably not more than 20 μsec. The energyrequired for the irradiation of the image-recording material preferablyranges from 10 to 300 mJ/cm². If the energy for the exposure is tooweak, the image-recording layer is never sufficiently cured. On theother hand, if it is too strong, the image-recording layer is subjectedto laser ablation and the images may thus be damaged.

In the present invention, the imagewise exposure may be carried out bymaking light beams from light sources overlap with one another. The term“overlap” herein used means that the secondary scanning pitch width issmaller than the beam diameter. When the beam diameter is expressed interms of the half band width of the beam strength (FWHM), the degree ofsuch overlap can quantitatively be defined by FWHM/ the secondaryscanning pitch width (overlap coefficient). In the present invention,this overlap coefficient is preferably not less than 0.1.

The scanning system for the light source of the exposure device used inthe invention is not particularly restricted and may be, for instance,the drum external surface scanning system, the drum inner face scanningsystem and the flat-bed scanning system. Moreover, the light source maybe a mono-channel or multi-channel type one, but a multi-channel typeone is preferably used, in case of the drum external surface scanningsystem.

In the present invention, the image-forming material may be developedimmediately after the imagewise exposure, but the material may beheat-treated between the exposure and developing steps. Thisheat-treatment is preferably carried out at a temperature ranging from60 to 150° C. for 5 seconds to 5 minutes.

The foregoing heat-treatment can appropriately be selected from avariety of known methods. Specific examples thereof include a methodcomprising heating the image-forming material while bringing thematerial into contact with a panel heater or a ceramic heater and anon-contact heating method using a lamp or hot air. The use of theforegoing heat-treatment would permit the reduction of the quantity ofthe laser energy required for irradiating the material with laser raysto thus record images on the material.

Moreover, the method of the invention may likewise comprise preliminarywater-washing step prior to the developing step to thus remove theprotective layer. Tap water is, for instance, used in the preliminarywater-washing step.

Then the image-forming material thus developed may be subjected tovarious post-treatments such as washing with water, and treatments witha rinsing liquid containing, for instance, a surfactant and/or with adesensitizing gum solution containing, for instance, gum Arabic or astarch derivative, as disclosed in, for instance, J.P. KOKAI Nos. Sho54-8002, Sho 55-115045 and Sho 59-58431. The post-treatment of theimage-forming material of the invention may comprise a variety ofcombinations thereof.

In the image-forming method of the invention, it is quite effective toheat the entire surface of the image-forming material after thedevelopment or to subject the entire surface of the material to lightexposure.

The heat-treatment after the development may be carried out under quiresevere conditions. The treatment is in general conducted at a heatingtemperature ranging from 200 to 500° C. If the heating temperature afterthe development is low, it is not possible to enjoy a sufficientimage-reinforcing effect, while if it is too high, problems may arisesuch that the substrate is deteriorated and that the image areas may bethermally decomposed.

If the image-forming material of the present invention is a lithographicprinting plate precursor, the lithographic printing plate prepared bythe foregoing treatments is fitted to an offset printing press and usedfor preparing a large number of printed matters. A plate cleaner may beused during printing operations for the removal of any contaminant onthe printing plate. Such a plate cleaner usable herein may be anyconventionally known one for PS (pre-sensitized) plates, for instance,those available from Fuji Photo Film Co., Ltd. such as CL-1, CL-2, CP,CN-4, CN, CG-1, PC-1, SR and IC.

EXAMPLES

The image-forming method according to the present invention which makesuse of a lithographic printing plate precursor as an image-formingmaterial will hereunder be described in more detail with reference tothe following Examples, but the present invention is not restricted tothese specific Examples at all.

Examples 1 to 13 and Comparative Examples 1 to 6

[Preparation of Substrate]

<Aluminum Plate>

A molten metal was prepared using an aluminum alloy comprising Si: 0.06%by weight, Fe: 0.30% by weight, Cu: 0.001% by weight, Mn: 0.001% byweight, Mg: 0.001% by weight, Zn: 0.001% by weight, Ti: 0.03% by weightand the balance of Al and inevitable impurities, followed by thetreatment and filtration of the molten metal and subsequent preparationof an ingot having a thickness of 500 mm and a width of 1200 mmaccording to the DC casting method. After scraping the surface of theingot in an average thickness of 10 mm using a facing device, the ingotwas subjected to soaking at 550° C. for about 5 hours and it was formedinto a rolled sheet having a thickness of 2.7 mm in a hot rolling millwhen the temperature of the ingot was reduced to 400° C. Further, therolled sheet was heat-treated at 500° C. using a continuous annealingmachine and then processed into a sheet having a thickness of 0.24 mmaccording to the cold rolling to thus give an aluminum plate satisfyingthe requirements for JIS 1050 Material. The width of the resultingaluminum plate was adjusted to 1030 mm and then subjected to thefollowing surface-treatments.

<Surface-Treatments>

The surface-treatment was conducted by continuously carrying out thevarious kinds of treatments (a) to (j) specified below. In this respect,the aluminum plate was subjected to liquid-drainage using a nip rollerafter each treatment and water-washing.

(a) Mechanical Surface-Graining Treatment

The aluminum plate was mechanically surface-roughened using a rotatingroller-like nylon brush, while supplying a suspension comprising waterand an abrasive (pumice stone) having a specific gravity of 1.12 as anabrasion slurry onto the surface of the plate. The average and maximumparticle sizes of the abrasive were found to be 30 μm and 100 μm,respectively. The nylon brush was produced from 6/10 nylon and thelength and diameter of the bristles thereof were found to be 45 mm and0.3 mm, respectively. The nylon brush was prepared by making holes on astainless steel cylinder having a diameter φ of 300 mm and denselyplanting such bristles in the cylinder. Three such rotating brushes wereused in this Example. The distance between two support rolls (φ: 200 mm)below the brushes was set at a level of 300 mm. The roller brushes werepressed against the aluminum plate in such a manner that the load of thedriving motor for rotating the brushes was equal to a level of 7 kWhigher than that observed when the brushes were not pressed against theplate. The rotational direction of the brushes was identical to themoving direction of the aluminum plate. The rotational number of thebrushes was set at 200 rpm.

(b) Alkali-Etching Treatment

The aluminum plate thus treated was then subjected to an etchingtreatment by spraying the plate with an aqueous solution containing 2.6%by weight of caustic soda and 6.5% by weight of aluminum ions andmaintained at 70° C. for the dissolution of 10 g/m² of aluminum.Subsequently, the plate was washed with water by spraying.

(c) Desmutting Treatment

The aluminum plate was desmutted by spraying the plate with an aqueousnitric acid solution having a concentration of 1% by weight (containing0.5% by weight of aluminum ions) at a temperature of 30° C. and then theplate was washed with water by spraying. The nitric acid aqueoussolution used in the desmutting treatment was the waste liquor generatedin the step of the electrochemical surface-roughening treatment using analternating current in a nitric acid aqueous solution.

(d) Electrochemical Surface-Roughening Treatment

The aluminum plate was subjected to a continuous electrochemicalsurface-roughening treatment using an AC voltage of 60 Hz. Theelectrolyte used in this treatment was an aqueous solution containing10.5 g/L of nitric acid (containing 5 g/L of aluminum ions and 0.007% byweight of ammonium ions) and having a temperature of 50° C. Theelectrochemical surface-roughening treatment was carried out using atrapezoidal rectangular waved alternating current whose TP or the timerequired for achieving the peak current value starting from zero currentwas 0.8 msec and a duty ratio of 1:1 as the wave form of the alternatingpower source and a carbon electrode as a counter electrode. A ferriteelectrode was used as a secondary anode.

The current density was found to be 30 A/dm² at the peak current and theelectricity was found to be 220 C/dm² as expressed in terms of the totalanode time electricity of the aluminum plate. To the secondary anode, 5%of the current supplied from the power source was branched. Thereafter,the plate was washed with water through spraying.

(e) Alkali-Etching Treatment

The aluminum plate was etched through spraying at 32° C. using anaqueous solution containing 26% by weight of caustic soda and 6.5% byweight of aluminum ions to thus dissolve the aluminum plate in an amountof 0.50 g/m², followed by the removal of the smut components mainlycomprising aluminum hydroxide generated during the precedingelectrochemical surface-roughening treatment (d) using an alternatingcurrent and the dissolution of the edge portions of pits formed duringthe step to thus make the edge portions smooth. Thereafter, the platewas washed with water through spraying.

(f) Desmutting Treatment

The aluminum plate thus treated was desmutted at 30° C. by spraying anaqueous solution (containing 4.5% by weight of aluminum ions) having anitric acid concentration of 15% by weight and thereafter, it was washedwith water through spraying. The nitric acid solution used in thisdesmutting treatment was the waste liquor generated in the step of theelectrochemical surface-roughening treatment using an alternatingcurrent in a nitric acid aqueous solution.

(g) Electrochemical Surface-Roughening Treatment

The aluminum plate was subjected to a continuous electrochemicalsurface-roughening treatment using an AC voltage of 60 Hz. Theelectrolyte used in this treatment was an aqueous solution containing5.0 g/L of hydrochloric acid (containing 5 g/L of aluminum ions) andhaving a temperature of 35° C. The electrochemical surface-rougheningtreatment was carried out using a trapezoidal rectangular wavedalternating current whose TP or the time required for achieving the peakcurrent value starting from zero current was 0.8 msec and a duty ratioof 1:1 as the wave form of the alternating power source and a carbonelectrode as a counter electrode. A ferrite electrode was used as asecondary anode.

The current density was found to be 25 A/dm² at the peak current and theelectricity was found to be 50 C/dm² as expressed in terms of the totalanode time electricity of the aluminum plate. Thereafter, the plate waswashed with water through spraying.

(h) Alkali-Etching Treatment

The aluminum plate was etched through spraying at 32° C. using anaqueous solution containing 26% by weight of caustic soda and 6.5% byweight of aluminum ions to thus dissolve the aluminum plate in an amountof 0.10 g/m², followed by the removal of the smut components mainlycomprising aluminum hydroxide generated during the precedingelectrochemical surface-roughening treatment (g) using an alternatingcurrent and the dissolution of the edge portions of pits formed duringthe step to thus make the edge portions smooth. Thereafter, the platewas washed with water through spraying.

(i) Desmutting Treatment

The aluminum plate thus treated was desmutted at 60° C. by spraying anaqueous solution (containing 0.5% by weight of aluminum ions) having asulfuric acid concentration of 25% by weight and thereafter, it waswashed with water through spraying.

(j) Anodization Treatment

Then the aluminum plate was anodized to thus give a substrate forlithographic printing plate. Sulfuric acid solutions were used aselectrolytes supplied to a first and second electrolyzation zones. Bothof these electrolytes had a sulfuric acid concentration of 170 g/L(containing 0.5% by weight of aluminum ions) and they were maintained at38° C. Thereafter, the plate was washed with water through spraying. Theamount of the anodized film ultimately formed was found to be 2.7 g/m².

The Ra value of the substrate thus obtained after the foregoingtreatments was found to be 0.45.

[Under Coat]

Then the following under coat liquid was applied onto the aluminumsubstrate using a wire bar and the liquid thus applied was dried at 90°C. for 30 seconds in a warm air dryer. The coated amount determinedafter drying was found to be 10 mg/m².

<Under Coat Liquid> Ethyl acrylate/sodium2-acrylamide-2-methyl-1-propanesulfonate 0.1 g (molar ratio: 75/15)copolymer 2-Aminoethyl-phosphonic acid 0.1 g Methanol  50 g Deionizedwater  50 g[Image-Recording Layer]

Then the following coating liquid [P-1] for forming an image-recordinglayer was prepared and applied onto the aluminum substrate provided withthe under coat using a wire bar coater. The liquid thus applied wasdried at 122° C. for 43.5 seconds in a warm air dryer to thus form animage-recording layer. The coated amount thereof determined after dryingwas found to be 1.4 g/m².

<Liquid [P-1] for Image-Recording Layer> Infrared light absorber (IR-1)0.08 g Polymerization initiator (OS-1) 0.25 g Di-pentaerythritolhexa-acrylate 1.00 g Binder polymer (BT-1) 1.00 g Chloride salt of EthylViolet 0.04 g Fluorine atom-containing surfactant (Megafac F-780-Favailable 0.03 g from Dainippon Ink and Chemicals, Inc.) Methyl ethylketone 10.4 g Methanol 4.83 g 1-Methoxy-2-propanol 10.4 g

The following are structural formulas of the infrared light absorber(IR-1), polymerization initiator (OS-1) and binder polymer (BT-1) usedin the foregoing coating liquid for forming the image-recording layer:

Infrared Light Absorber (IR-1)

[Protective Layer (Overcoat Layer)]

A mixed aqueous solution containing polyvinyl alcohol (degree ofsaponification: 98 mole %; degree of polymerization: 500) and polyvinylpyrrolidone (PVP K-30 available from BASF Company) was coated on thesurface of the foregoing image-recording layer using a wire bar coaterand dried at 125° C. for 75 seconds in a warm air dryer. The content ofthe PVA in the aqueous solution was set at 85% by weight and the coatedamount (as determined after drying) of the solution was found to be 2.45g/m².

<Developer>

The following components were dissolved in water to prepare eachcorresponding developer: a mol/L of a carbonate; b mol/L of abicarbonate; c g/L of a surfactant; d g/L of an additive and 2 g/L oftetra-sodium ethylenediamine-tetra-acetate (a chelating agent).

TABLE 1 Alkaline Alkaline Alkaline Surfac- pH Conductivity agent 1 mol/Lagent 2 mol/L agent 3 mol/L tant wt % Additive g/L [25° C.] [25° C., mS]Developer 1 K₂CO₃ 0.17 KHCO₃ 0.038 None Y-1 5 None 10.5 31 Developer 2K₂CO₃ 0.3 KHCO₃ 0.067 None Y-1 5 None 10.5 52.1 Developer 3 K₂CO₃ 0.59KHCO₃ 0.13 None Y-1 5 None 10.5 95.4 Developer 4 Na₂CO₃ 0.4 NaHCO₃ 0.09None Y-1 5 None 10.5 55.3 Developer 5 K₂CO₃ 0.3 KHCO₃ 0.067 None Y-1 2None 10.5 52 Developer 6 K₂CO₃ 0.3 KHCO₃ 0.067 None Y-1 8 None 10.5 52.5Developer 7 K₂CO₃ 0.13 KHCO₃ 0.029 None Y-1 5 K citrate 12 10.5 31.6Developer 8 K₂CO₃ 0.13 KHCO₃ 0.029 None Y-1 5 NaCl 7 10.5 34.2 Developer9 K₂CO₃ 0.3 KHCO₃ 0.067 None Y-2 5 None 10.5 31.5 Developer 10 K₂CO₃ 0.3KHCO₃ 0.067 None Y-13 5 None 10.5 31.4 Developer 11 K₂CO₃ 0.3 KHCO₃0.067 KOH 0.015 Y-1 5 None 11.4 57.1 Developer 12 K₂CO₃ 0.11 KHCO₃ 0.13None Y-1 5 None 9.8 46.2 Developer 13 K₂CO₃ 0.08 KHCO₃ 0.25 None Y-1 5None 9.1 39.1 Com. Dev.* 1 K₂CO₃ 0.13 KHCO₃ 0.029 None Y-1 5 None 10.525.3 Com. Dev.* 2 K₂CO₃ 0.65 KHCO₃ 0.145 None Y-1 5 None 10.5 105 Com.Dev.* 3 K₂CO₃ 0.3 KHCO₃ 0.067 None Y-1 0.5 None 10.5 52.1 Com. Dev.* 4K₂CO₃ 0.3 KHCO₃ 0.067 None Y-1 11 None 10.5 52.1 Com. Dev.* 5 KOH 0.1None None Y-1 5 None 13 32 Com. Dev.* 6 KOH 0.0001 None None Y-1 5 None10.5 3.5 Com. Dev.*: Comparative Developer[Evaluation]

The developing rate of non-image areas with an alkaline developer wasdetermined as an indication for the evaluation of the developing abilityand the penetration rate of the alkaline developer into theimage-recording layer was likewise determined as an indication for theevaluation of the printing durability.

The methods for determining the “developing rate of non-image areas withan alkaline developer” and the “penetration rate of the alkalinedeveloper into the image-recording layer” used in the invention will bedescribed in detail below.

<Determination of Developing Rate of Non-Image Areas with AlkalineDeveloper>

The term “developing rate of non-image areas with an alkaline developer”herein used is defined to be the thickness (m) of the image-recordinglayer (non-image area) divided by the time (sec) required for thedevelopment thereof.

The method for determining the developing rate used in the inventioncomprises, as shown in FIG. 1, immersing a sample which comprised analuminum substrate provided thereon with an un-exposed image-recordinglayer in an alkaline developer (30° C.) and inspecting theimage-recording layer for the dissolution behavior thereof by a DRMinterference spectrophotometer. FIG. 1 shows a schematic diagram forillustrating such a DRM interference spectrophotometer for thedetermination of the dissolution behavior of the image-recording layer.In the present invention, any change in the film thickness was detectedby the interference method using light rays of 640 nm. In case where thedissolution behavior is the development, free of any swelling, from thesurface of the image-recording layer, the film thickness is graduallyreduced with the elapse of the developing time and a characteristicinterference pattern proportional to the thickness can accordingly beobtained. Moreover, in case where the dissolution behavior is thedissolution accompanied by swelling (dissolution with release of film),the thickness of the layer varies due to the penetration of thedeveloper and therefore, there is not observed any definite or clearinterference pattern at all.

When the determination is continued under these conditions, theimage-recording layer is completely removed and accordingly, thedevelopment rate can be determined using the equation specified below onthe basis of the time (sec) required for making the film thickness zero(or the time required for the completion of the development) and thethickness of the image-recording layer (μm). Thus, it can be judged asfollows: the higher the development rate, the easier the removal of thefilm with the developer and the better the developing properties of thedeveloper.Development Rate (of un-exposed area)=[(Thickness (μm) ofimage-recording layer)/(Time (sec) required for the completion ofdevelopment)]

To make clear the correspondency between the practical quality and thetheoretical one, tests were conducted for examining developingproperties of plate materials (see the section concerning the evaluationof developing properties).

<Determination of Penetration Rate of Alkaline Developer intoImage-Recording Layer>

Moreover, the term “penetration rate of alkaline developer intoimage-recording layer” herein used is defined to be a value showing therate of change in the electrostatic capacity (F) observed when theforegoing image-recording layer is formed on an electrically conductivesubstrate and the resulting assembly is immersed in a developer.

An example of the method for determining the electrostatic capacityserving as a tentative criterion for the evaluation of the penetrationrate herein used comprises, as shown in FIG. 2, immersing an aluminumsubstrate serving as an electrode and provided thereon with an exposed(using Trendsetter 3224VX equipped with a water-cooled 40 W infraredsemiconductor laser available from Creo Inc., under the followingconditions: resolution: 175 lpi; rotational number of outer drum: 150rpm; output: 8 W) and cured image-recording layer in an alkalinedeveloper (28° C.); connecting the aluminum substrate to a leading wire,providing a usual electrode as the counterpart electrode and applying anelectric voltage between these electrodes. After the application of theelectric voltage, the developer penetrates into the interface betweenthe substrate and the image-recording layer and thus the electrostaticcapacity is changed with the elapse of time.

The desired developer-penetration rate can be determined according tothe following equation on the basis of the time (s) required till theelectrostatic capacity causes a change and the thickness (μm) of theimage-recording layer. In this respect, it can be judged as follows: thelower the penetration rate, the lower the penetration ability of thedeveloper into the layer.Penetration rate of developer (into un-exposed area)=[(Thickness (μm) ofthe image-recording layer)/(Time (s) required the electrostatic capacitychange to reach a constant level)]

To make clear the correspondency between the practical quality and thetheoretical one, tests were conducted for examining the printingdurability of the resulting plate materials (see the section concerningthe evaluation of printing durability).

The image-recording layer of the lithographic printing plate precursorused in the present invention should have the following physicalproperties: the developing rate of the un-exposed portion with respectto an alkaline developer of preferably not less than 80 nm/sec, morepreferably 80 to 400 nm/sec and further preferably 90 to 200 nm/sec. Inaddition, the penetration rate of alkaline developer observed forexposed areas is preferably not more than 100 nF/sec, more preferablynot more than 90 nF/sec and further preferably not more than 80 nF/sec.

(Evaluation of Developing Ability (or Developing Properties))

The developing ability of the practical non-image area was observed bydeveloping the same at 30° C. for 12 seconds using LP-1310HII availablefrom Fuji Photo Film Co., Ltd.

(Evaluation of Printing Durability)

The resulting lithographic printing plate precursor was imagewiseexposed to light using Trendsetter 3244VX equipped with a water-cooled40 W infrared light-emitting semiconductor laser available from CreoCompany, under the conditions of: resolution: 175 lpi and rotationalnumber of outer drum: 150 rpm, while changing the output by 0.15 each ata time, as expressed in terms of log E, within the range of from 0 to 8W. In this connection, the exposure was carried out at 25° C. and 50%RH. After the exposure to light rays, the exposed precursor was washedwith tap water to remove the protective layer and then the precursor wasdeveloped at 30° C. for 12 seconds using LP-1310HII available from FujiPhoto Film Co., Ltd. A 1:1 water diluted solution of FP-2W availablefrom Fuji Photo Film Co., Ltd. was used as a finisher.

The resulting lithographic printing plate was fitted to a printing pressLITHRON 26 available from Komori Corporation to thus obtain printedmatters and the number of possible printed matters was used as anindication for the printing durability.

(pH Reduction Due to Carbon Dioxide in Air)

Each developer was charged to LP-1310HII available from Fuji Photo FilmCo., Ltd. and any pH change was determined after allowing the platematerial to stand for one day.

(Evaluation of Scum-Formation During Development)

In the foregoing developer (one liter), 20 m² of the foregoing coatedlight-sensitive material was developed, thereafter the developer wasallowed to stand for one month and then the presence of any precipitatedscum was examined. These results are summarized in the following Table2.

TABLE 2 Dev. rate Penetration Printing of Non- rate durability Dev.image of image No. of pH Change Ex. No. area Developing area Printedover Dev. No. Used (μm/sec) Properties (nF/sec) matters 24 hr Scum  1  1115 ◯ 45 100,000 0.1 ◯  2  2 140 ◯ 50 100,000 0.1 ◯  3  3 145 ◯ 6590,000 0.1 ◯  4  4 140 ◯ 65 100,000 0.1 ◯  5  5 95 ◯ 40 110,000 0.1 Δ  6 6 140 ◯ 65 90,000 0.1 ◯  7  7 115 ◯ 50 100,000 0.1 ◯  8  8 115 ◯ 55100,000 0.1 ◯  9  9 130 ◯ 55 100,000 0.1 ◯ 10 10 90 ◯ 60 100,000 0.1 Δ11 11 145 ◯ 80 90,000 0.15 ◯ 12 12 105 ◯ 50 100,000 0.1 ◯ 13 13 90 ◯ 50100,000 0.1 ◯  1*  1** 75 Residual film 40 100,000 0.1 ◯  2*  2** 70Residual film 40 100,000 0.1 ◯  3*  3** 20 Residual film 35 110,000 0.1X  4*  4** 140 ◯ 125 70,000 0.1 X  5*  5** 145 ◯ 175 70,000 0.4 ◯  6* 6** 5 Residual film 40 110,000 0.6 X *Comparative Example No.**Comparative Developer No.

In Table 2, ◯ appearing in the evaluation of the developing propertiesmeans that any residual film was not observed at all; and the formationof scum during development was evaluated on the basis of the followingcriteria: ◯: there was not observed any precipitate; Δ: there wasobserved a trace amount of precipitates; and X: there was observed alarge amount of precipitates.

Examples 14 to 26 and Comparative Examples 7 to 12

A substrate was prepared and surface-treated by repeating the sameprocedures used in Examples 1 to 13 and then an under coat, animage-recording layer and a protective layer were formed thereonaccording to the same procedures used in Examples 1 to 13. The resultinglight-sensitive lithographic printing plate was developed with adeveloper specified in the following Table 3 and then the plate wasinspected for the printing durability, the formation of scum duringdevelopment and the like according to the same procedures used inExamples 1 to 11.

<Developer>

Each developer was prepared by dissolving the following components inwater: a mole/L of a carbonate; b mole/L of a bicarbonate; c g/L of asurfactant; d g/L of an additive; and 2 g/L of tetra-sodiumethylenediamine-tetra-acetate (a chelating agent).

TABLE 3 Conduc- Alkaline Alkaline Alkaline Surfac- Addi- pH tivity agent1 mol/L agent 2 mol/L agent 3 mol/L tant wt % tive g/L [25 ° C.] [25°C., mS] Developer 14 K₂CO₃ 0.17 KHCO₃ 0.038 None II-13 5 None 10.4 34.2Developer 15 K₂CO₃ 0.3 KHCO₃ 0.067 None II-13 5 None 10.4 55.2 Developer16 K₂CO₃ 0.59 KHCO₃ 0.13 None II-13 5 None 10.4 98.5 Developer 17 Na₂CO₃0.4 NaHCO₃ 0.09 None II-13 5 None 10.4 58.4 Developer 18 K₂CO₃ 0.3 KHCO₃0.067 None II-13 2 None 10.4 55.1 Developer 19 K₂CO₃ 0.3 KHCO₃ 0.067None II-13 8 None 10.4 55.6 Developer 20 K₂CO₃ 0.13 KHCO₃ 0.029 NoneII-13 5 K 12 10.4 34.7 citrate Developer 21 K₂CO₃ 0.13 KHCO₃ 0.029 NoneII-13 5 NaCl 7 10.4 37.3 Developer 22 K₂CO₃ 0.3 KHCO₃ 0.067 None II-22 5None 10.4 34.6 Developer 23 K₂CO₃ 0.3 KHCO₃ 0.067 None I-23 5 None 10.434.5 Developer 24 K₂CO₃ 0.3 KHCO₃ 0.067 KOH 0.015 II-13 5 None 11.4 60.2Developer 25 K₂CO₃ 0.11 KHCO₃ 0.13 None II-13 5 None 9.8 49.3 Developer26 K₂CO₃ 0.08 KHCO₃ 0.25 None II-13 5 None 9.1 42.2 Com. Dev.* 7 K₂CO₃0.13 KHCO₃ 0.029 None II-13 5 None 10.4 28.4 Com. Dev.* 8 K₂CO₃ 0.65KHCO₃ 0.145 None II-13 5 None 10.4 108.1 Com. Dev.* 9 K₂CO₃ 0.3 KHCO₃0.067 None II-13 0.5 None 10.4 55.2 Com. Dev.* 10 K₂CO₃ 0.3 KHCO₃ 0.067None II-13 11 None 10.4 55.2 Com. Dev.* 11 KOH 0.1 None None II-13 5None 13 35.1 Com. Dev.* 12 KOH 0.0001 None None II-13 5 None 10.4 6.6Com. Dev.*: Comparative Developer[Evaluation ]

TABLE 4 Printing Dev. rate Penetration durability of Non- rate No. ofDev. image of image Printed pH Change Ex. No. area Developing areamatters over Dev. No. Used (μm/sec) Properties (nF/sec) (×10⁴) 24 hrScum 14 14 105 ◯ 50 100,000 0.1 ◯ 15 15 135 ◯ 55 100,000 0.1 ◯ 16 16 145◯ 60 90,000 0.1 ◯ 17 17 135 ◯ 60 100,000 0.1 ◯ 18 18 95 ◯ 45 110,000 0.1Δ 19 19 130 ◯ 65 90,000 0.1 ◯ 20 20 110 ◯ 50 100,000 0.1 ◯ 21 21 115 ◯55 100,000 0.1 ◯ 22 22 135 ◯ 50 100,000 0.1 ◯ 23 23 90 ◯ 60 100,000 0.1Δ 24 24 140 ◯ 80 90,000 0.15 ◯ 25 25 105 ◯ 50 100,000 0.1 ◯ 26 26 90 ◯50 100,000 0.1 ◯  7*  7** 80 Residual film 50 100,000 0.1 ◯  8*  8** 75Residual film 50 100,000 0.1 ◯  9*  9** 25 Residual fllm 35 110,000 0.1X 10* 10** 140 ◯ 125 70,000 0.1 X 11* 11** 145 ◯ 175 70,000 0.4 ◯ 12*12** 10 Residual film 40 110,000 0.6 X *Comparative Example No.**Comparative Developer No.

In Table 2, ◯ appearing in the evaluation of the developing propertiesmeans that any residual film was not observed at all; and the formationof scum during development was evaluated on the basis of the followingcriteria: ◯: there was not observed any precipitate; Δ: there wasobserved a trace amount of precipitates; and X: there was observed alarge amount of precipitates.

EFFECTS OF THE INVENTION

The developer and image-forming method according to the presentinvention can ensure sufficient developing properties or a satisfactorydeveloping ability at a low pH wherein the image-forming material ishardly damaged. Accordingly, they permit the simultaneous achievement ofgood printing durability and a good developing ability of animage-forming material. Further, the developing activity of thedeveloper is not hardly reduced due to the action of carbon dioxide andtherefore, it does not suffer from a problem originated from the scumformed during development.

1. A developer comprising at least one carbonate and at least onehydrogen carbonate, and at least one surfactant selected from the groupconsisting of nonionic aromatic ether type surfactants represented bythe following general formula (1-A) or (1-B) and anionic surfactantsselected from the group consisting of compounds having at least one ofanionic groups derived from sulfonic acid or anionic groups derived fromsulfuric acid monoesters in an amount ranging from 1.0 to 10% by weight;and having a pH value ranging from 8.5 to 11.5 and an electricalconductivity x falling within the range: 30<x <100 mS/cm:

wherein, R₁ and R₂ represent a hydrogen atom or an organic group having1 to 100 carbon atoms, respectively: p and q represent 1 or 2,respectively: Y₁ and Y₂ represent a single bond or an alkylene grouphaving 1 to 10 carbon atoms, respectively: r and s are 0 or an integerranging from 1 to 100, respectively, provided that r and s cannotsimultaneously represent 0 and that when either r or s is 0, r and scannot represent 1: and r′ and s′ are 0 or an integer ranging from 1 to100, respectively, provided that r′ and s′ cannot simultaneouslyrepresent 0 and that when either r′ or s′ is
 0. r′ and s′ cannotrepresent
 1. 2. The developer of claim 1 wherein the anionic surfactantis a compound having at least one of anionic groups derived fromsulfonic acid or anionic groups derived from sulfuric acid monoestersand at least one substituted or unsubstituted aromatic group.
 3. Thedeveloper of claim 1 wherein the carbonate is at least one memberselected from the group consisting of carbonates of inorganic alkalisand the hydrogen carbonate is at least one member selected from thegroup consisting of hydrogen carbonates of inorganic alkalis.
 4. Thedeveloper of claim 1 wherein the carbonate is at least one memberselected from the group consisting of potassium carbonate, sodiumcarbonate and ammonium carbonate and the hydrogen carbonate is at leastone member selected from the group consisting of potassium hydrogencarbonate, sodium hydrogen carbonate and ammonium hydrogen carbonate. 5.The developer of claim 1 wherein the developer further comprises atleast one compound selected from the group consisting of alkali metalsalts of organic acids and alkali metal salts of inorganic acids.
 6. Animage-forming method comprising the steps of imagewise exposing anegative-working image-forming material which comprises a substrateprovided thereon with an image-recording layer comprising an infraredlight absorber, a polymerization initiator, an ethylenically unsaturatedbond-containing monomer and a binder polymer; and then developing theimagewise exposed image-forming material with the developer as set forthin claim 1.